Communication system

ABSTRACT

A narrow-bandwidth terminal device performs radio communication at a bandwidth narrower than a system bandwidth. The narrow-bandwidth terminal device in an idle state camps on a cell, and performs discontinuous reception of a signal transmitted from the cell. The terminal device also determines a reception condition of the signal, for example, whether the signal can be received. When it is determined that the signal cannot be received, the narrow-bandwidth terminal device moves out of a coverage area of the cell while continuing to perform the discontinuous reception. When it is determined that a discontinuous reception timer has been completed, the narrow-bandwidth terminal device continues to perform the discontinuous reception.

TECHNICAL FIELD

The present invention relates to a communication system in which radiocommunication is performed between a communication terminal device and abase station device.

BACKGROUND ART

The 3rd generation partnership project (3GPP), the standard organizationregarding the mobile communication system, is studying communicationsystems referred to as long term evolution (LTE) regarding radiosections and system architecture evolution (SAE) regarding the overallsystem configuration including a core network and a radio accessnetwork, which will be hereinafter collectively referred to as a networkas well (for example, see Non-Patent Documents 1 to 16). Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

As the access scheme of the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. Further, differently from the wideband code division multipleaccess (W-CDMA), circuit switching is not provided but a packetcommunication system is only provided in the LTE.

The decisions by 3GPP regarding the frame configuration in the LTEsystem described in Non-Patent Document 1 (Chapter 5) will be describedwith reference to FIG. 1. FIG. 1 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 1, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal per radio frame. The synchronizationsignals are classified into a primary synchronization signal (P-SS) anda secondary synchronization signal (S-SS).

Non-Patent Document 1 (Chapter 5) describes the decisions by 3GPPregarding the channel configuration in the LTE system. It is assumedthat the same channel configuration is used in a closed subscriber group(CSG) cell as that of a non-CSG cell.

A physical broadcast channel (PBCH) is a channel for downlinktransmission from a base station to a user equipment. A BCH transportblock is mapped to four subframes within a 40 ms interval. There is noexplicit signaling indicating 40 ms timing.

A physical control format indicator channel (PCFICH) is a channel fordownlink transmission from a base station to a user equipment. ThePCFICH notifies the number of orthogonal frequency division multiplexing(OFDM) symbols used for PDCCHs from the base station to the userequipment. The PCFICH is transmitted per subframe.

A physical downlink control channel (PDCCH) is a channel for downlinktransmission from a base station to a user equipment. The PDCCH notifiesof the resource allocation information for downlink shared channel(DL-SCH) being one of the transport channels described below, resourceallocation information for a paging channel (PCH) being one of thetransport channels described below, and hybrid automatic repeat request(HARQ) information related to DL-SCH. The PDCCH carries an uplinkscheduling grant. The PDCCH carries acknowledgement (Ack)/negativeacknowledgement (Nack) that is a response signal to uplink transmission.The PDCCH is referred to as an L1/L2 control signal as well.

A physical downlink shared channel (PDSCH) is a channel for downlinktransmission from a base station to a user equipment. A downlink sharedchannel (DL-SCH) that is a transport channel and a PCH that is atransport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) is a channel for downlinktransmission from a base station to a user equipment. A multicastchannel (MCH) that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) is a channel for uplinktransmission from a user equipment to a base station. The PUCCH carriesAck/Nack that is a response signal to downlink transmission. The PUCCHcarries a channel quality indicator (CQI) report. The CQI is qualityinformation indicating the quality of received data or channel quality.In addition, the PUCCH carries a scheduling request (SR).

A physical uplink shared channel (PUSCH) is a channel for uplinktransmission from a user equipment to a base station. An uplink sharedchannel (UL-SCH) that is one of the transport channels is mapped to thePUSCH.

A physical hybrid ARQ indicator channel (PHICH) is a channel fordownlink transmission from a base station to a user equipment. The PHICHcarries Ack/Nack that is a response signal to uplink transmission. Aphysical random access channel (PRACH) is a channel for uplinktransmission from the user equipment to the base station. The PRACHcarries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: a cell-specific reference signal (CRS), an MBSFNreference signal, a data demodulation reference signal (DM-RS) being aUE-specific reference signal, a positioning reference signal (PRS), anda channel-state information reference signal (CSI-RS). The physicallayer measurement objects of a user equipment include reference signalreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described. A broadcast channel (BCH) among the downlinktransport channels is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to be broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of multimediabroadcast multicast service (MBMS) services (MTCH and MCCH) inmulti-cell transmission. The MCH supports semi-static resourceallocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels. TheUL-SCH supports dynamic or semi-static resource allocation. The UL-SCHis mapped to the physical uplink shared channel (PUSCH).

A random access channel (RACH) is limited to control information. TheRACH involves a collision risk. The RACH is mapped to the physicalrandom access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nack” to the transmitter. The transmitter that has received“Nack” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described. A broadcast control channel (BCCH) is a downlink channelfor broadcast system control information. The BCCH that is a logicalchannel is mapped to the broadcast channel (BCH) or downlink sharedchannel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the ceil location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin the case where the user equipments have no RRC connection with thenetwork. In the downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In the uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a user equipment and a network on apoint-to-point basis. The DCCH is used when the user equipment has anRRC connection. The DCCH is mapped to the uplink shared channel (UL-SCH)in uplink and mapped to the downlink shared channel (DL-SCH) indownlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an e-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below.

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed use are specified by an operator (hereinafter, alsoreferred to as a “cell for specific subscribers”). The specifiedsubscribers are allowed to access one or more cells of a public landmobile network (PLMN). One or more cells to which the specifiedsubscribers are allowed access are referred to as “CSG cell(s)”. Notethat access is limited in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID) and broadcasts “TRUE” in a CSG indication. The authorizedmembers of the subscriber group who have registered in advance accessthe CSG cells using the CSG ID) that is the access permissioninformation.

The CSG ID is broadcast by the CSG cell or cells. A plurality of CSG IDsexist in the LTE communication system. The CSG IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked based on an area composedof one or more cells. The locations are tracked for enabling trackingthe locations of user equipments and calling user equipments, in otherwords, incoming calling to user equipments even in an idle state. Anarea for tracking locations of user equipments is referred to as atracking area.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 3 discloses three different modes ofthe access to the HeNB and HNB. Specifically, an open access mode, aclosed access mode, and a hybrid access mode are disclosed.

The individual modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both of the open access mode andthe closed access mode.

In 3GPP, among all physical cell identities (PCIs) is a range of PCIsreserved by the network for use by CSG cells (see Chapter 10.5.1.1 ofNon-Patent Document 1). Division of the PCI range is also referred to asPCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to user equipments being served thereby. Being served by a basestation means taking the base station as a serving cell.

Non-Patent Document 4 discloses the basic operation of a user equipmentusing PCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. On the other hand, the user equipment that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 5 and 6). TheLTE-A is based on the LTE radio communication system and is configuredby adding several new techniques to the system.

Carrier aggregation (CA) is studied for the LTE-A system, in which twoor more component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

In the case where CA is configured, a UE has a single RRC connectionwith a network (NW). In RRC connection, one serving cell provides NASmobility information and security input. This cell is referred to as aprimary cell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

The new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 7.

The new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 7.

Furthermore, 3GPP is studying the use of small eNBs configuring smallcells to satisfy tremendous traffic in the future. In an exampletechnique under study, etc., a large number of small eNBs will beinstalled to configure a large number of small cells, thus increasingspectral efficiency and communication capacity. The specific techniquesinclude dual connectivity in which a UE communicates with two eNBsthrough connection thereto.

Furthermore, the need for machine-type communication (MTC) that enablescommunication even without any human manipulation of a UE is increasing.The MTC is used in many types of services including, for example,sensing, meter monitoring, and parcel tracking monitoring, etc.

It is assumed that the increasing need for the MTC will be followed bythe use of excessive number of MTC user equipments (MTC UEs). Thus, theMTC UEs require lower cost and longer life, 3GPP is studying a techniquefor reducing the cost of the MTC UEs.

Furthermore, the need for systems using an unlicensed spectrum that is aspectrum that has not been licensed, as a tool for complementing alicensed spectrum that is a spectrum that has been licensed isincreasing. Examples of the unlicensed spectrum include industrial,scientific and medical (ISM) bands used for wireless local area network(LAN), etc. 3GPP is studying Licensed-Assisted Access (LAA) using theunlicensed spectrum as a tool for complementing the licensed spectrum,with the LTE.

The traffic flow of a mobile network is on the rise, and thecommunication rate is also increasing. It is expected that thecommunication rate will be further increased when the operations of theLTE and the LTE-A are fully initiated, leading to an increase in trafficflow.

PRIOR-ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS36.300 V12.2.0-   Non-Patent Document 2: 3GPP TS36.304 V12.1.0-   Non-Patent Document 3: 3GPP S1-083461-   Non-Patent Document 4: 3GPP R2-082899-   Non-Patent Document 5: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 6: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 7: 3GPP TR 36.819 V11.2.0-   Non-Patent Document 8: 3GPP TS 36.141 V12.4.0-   Non-Patent Document 9: 3GPP TR36.888 V12.0.0-   Non-Patent Document 10: 3GPP R1-144563-   Non-Patent Document 11: 3GPP R1-144662-   Non-Patent Document 12: 3GPP R1-145101-   Non-Patent Document 13: 3GPP R1-143992-   Non-Patent Document 14: 3GPP TS36.213 V12.1.0-   Non-Patent Document 15: 3GPP R1-145132-   Non-Patent Document 16: 3GPP R1-144236

SUMMARY OF INVENTION Problems to be Solved by the Invention

Requirements for low cost MTC (LC-MTC) include reduced bandwidth,coverage enhancement, and power consumption reduction. LC-MTC UEs whosebandwidth is to be reduced have a problem with inability to receivesystem information broadcasted at the entire system bandwidth.

Furthermore, since the LC-MTC UEs whose coverage is to be enhancedsuffer degradation in reception quality from cells in the enhancedareas, execution of repeated transmission (i.e., repetition oftransmission) is being studied. However, since a paging and the systeminformation, etc. have not conventionally undergone the repeatedtransmission, there is a problem with absence of a method for repeatedtransmission and reception.

Furthermore, when the unlicensed spectrum is used for the LTE, a faircoexistence method with the other systems using the unlicensed spectrumis necessary. Thus, the LAA requires, for example, a function ofListen-before-talk (clear channel assessment) before data transmissionand a function of disabling continuous data communication for a longperiod. Furthermore, when nothing is transmitted from a cell, provisionof a signal for synchronizing with or measuring the unlicensed spectrumhas been proposed to enable a UE to synchronize with or measure theunlicensed spectrum.

However, such transmission of a signal requires avoidance of a collisionand ensuring the fairness with the other systems to enable thecoexistence. There is a problem with absence of such a fair coexistencemethod on the signal for synchronizing or measuring the unlicensedspectrum

The present invention has an object of providing a communication systemthat enables improvement in communication performance of a communicationterminal device when the communication system supports various services.

Means to Solve the Problems

A communication system of the present invention is a communicationsystem including a communication terminal device and a base stationdevice configuring at least one cell capable of radio communication withthe communication terminal device. The communication terminal deviceincludes a narrow-bandwidth terminal device that performs radiocommunication at a bandwidth narrower than a system bandwidth that canbe used by the cell. The narrow-bandwidth terminal device performsdiscontinuous reception for intermittently receiving a signaltransmitted from the cell and determines a reception condition of thesignal when the narrow-bandwidth terminal device is in an idle statewithin a coverage area of the cell. The narrow-bandwidth terminal devicemoves out of the coverage area of the cell while continuing to performthe discontinuous reception, when the reception condition of the signalsatisfies a predetermined moving condition.

Effects of the Invention

In the communication system of the present invention, when thenarrow-bandwidth terminal device is in an idle state within a coveragearea of a cell, it performs discontinuous reception of a signaltransmitted from the cell, and determines a reception condition of thesignal. When the reception condition of the signal satisfies a movingcondition, the narrow-bandwidth terminal device moves out of thecoverage area of the cell while continuing to perform the discontinuousreception. Accordingly, since the idle state can be maintained withoutinformation for reselecting, a cell, the narrow-bandwidth terminaldevice can receive a paging signal. Furthermore, the power consumptionof the narrow-bandwidth terminal device can be reduced. Furthermore,since the structure of the communication system can be simplified, amalfunction of the communication system can be reduced.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a radio frame foruse in an LTE communication system.

FIG. 2 is a block diagram showing the overall configuration of an LTEcommunication system 700 under discussion of 3GPP.

FIG. 3 is a block diagram showing the configuration of a user equipment71 shown in FIG. 2, which is a user equipment according to the presentinvention.

FIG. 4 is a block diagram showing the configuration of a base station 72shown in FIG. 2, which is a base station according to the presentinvention.

FIG. 5 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 6 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 7 shows the concept of a cell configuration when macro eNBs andsmall eNBs coexist.

FIG. 8 is an example flowchart indicating processes of a UE in anRRC_Idle state according to a conventional technique.

FIG. 9 is an example flowchart indicating processes of an LC-MTC UE inthe RRC_Idle state according to a first embodiment.

FIG. 10 is an example flowchart indicating processes of the LC-MTC UE inthe RRC_Idle state according to a first modification of the firstembodiment.

FIG. 11 is an example flowchart indicating processes of the LC-MTC UE inthe RRC_Idle state according to a second modification of the firstembodiment.

FIG. 12 illustrates an example method for repeated paging transmissionaccording to a third embodiment.

FIG. 13 illustrates an example method for repeated paging transmissionaccording to a first modification of the third embodiment.

FIG. 14 is an example sequence diagram when a subframe for repeatedpaging transmission is determined from among subframes excluding MBSFNsubframes according to a second modification of the third embodiment.

FIG. 15 illustrates an example frame configuration when subframes forinitial transmission of an EPDCCH are identical to subframes forrepeated transmission thereof.

FIG. 16 illustrates an example paging message according to theconventional technique.

FIG. 17 illustrates an example paging message according to a fourthembodiment.

FIG. 18 illustrates an example configuration of a subframe including aninitial transmission of an EPDCCH and the repeated transmissionaccording to a first modification of the fourth embodiment.

FIG. 19 illustrates an example configuration of a subframe including aninitial transmission of an EPDCCH and the repeated transmissionaccording to the first modification of the fourth embodiment.

FIG. 20 illustrates an example state in which a cell transmits DSs and aUE measures the DSs over an unlicensed spectrum according to a seventhembodiment.

FIG. 21 illustrates an example state in which a cell transmits DSs and aUE measures the DSs over the unlicensed spectrum according to theseventh embodiment.

FIG. 22 illustrates an example state in which a cell transmits DSs and aUE measures the DSs over the unlicensed spectrum according to a firstmodification of the seventh embodiment.

FIG. 23 illustrates example processes until data communication throughtransmission of DSs and measurement of a UE according to the firstmodification of the seventh embodiment.

FIG. 24 illustrates example processes until data communication throughtransmission of DSs and measurement of a UE according to the firstmodification of the seventh embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 700, which is under discussion of 3GPP. FIG. 2 willbe described. A radio access network is referred to as an evolveduniversal terrestrial radio access network (E-UTRAN) 70. A userequipment device (hereinafter, referred to as a “user equipment (UE)”)71 that is a communication terminal device is capable of radiocommunication with a base station device (hereinafter, referred to as a“base station (E-UTRAN Node B: eNB)”) 72 and transmits and receivessignals through radio communication.

The E-UTRAN is composed of one or a plurality of base stations 72,provided that a control protocol for a user equipment 71 such as a radioresource control (RRC), and user planes such as a packet dataconvergence protocol (PDCP), radio link control (RLC), medium accesscontrol (MAC), or physical layer (PHY) are terminated in the basestation 72.

The control protocol radio resource control (RRC) between the userequipment 71 and the base station 72 performs broadcast, paging, RRCconnection management, and the like. The states of the base station 72and the user equipment 71 in RRC are classified into RRC_Idle andRRC_Connected.

In RRC_Idle, public land mobile network (PLMN) selection, systeminformation (SI) broadcast, paging, cell re-selection, mobility, and thelike are performed. In RRC_Connected, the user equipment has RRCconnection and is capable of transmitting and receiving data to and froma network. In RRC_Connected, for example, handover (HO) and measurementof a neighbor cell are performed.

The base stations 72 are classified into eNBs 76 and Home-eNBs 75. Thecommunication system 700 includes an eNB group 72-1 including aplurality of eNBs 76 and a Home-eNB group 72-2 including a plurality ofHome-eNBs 75. A system, composed of an evolved packet core (EPC) being acore network and an E-UTRAN 70 being a radio access network, is referredto as an evolved packet system (EPS). The EPC being a core network andthe E-UTRAN 70 being a radio access network may be collectively referredto as a “network”.

The eNB 76 is connected to an MME/S-GW unit (hereinafter, also referredto as an “MME unit”) 73 including a mobility management entity (MME), aserving gateway (S-GW), or an MME and an S-GW by means of an S1interface, and control information is communicated between the eNB 76and the MME unit 73. A plurality of MME units 73 may be connected to oneeNB 76. The eNBs 76 are connected to each other by means of an X2interface, and control information is communicated between the eNBs 76.

The Home-eNB 75 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB75 and the MME unit 73. A plurality of Home-eNBs 75 are connected to oneMME unit 73. Or, the Home-eNBs 75 are connected to the MME units 73through a Home-eNB gateway (HeNBGW) 74. The Home-eNB 75 is connected tothe HeNBGW 74 by means of an S1 interface, and the HeNBGW 74 isconnected to the MME unit 73 by means of an S1 interface.

One or a plurality of Home-eNBs 75 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface.

The MME units 73 and HeNBGW 74 are entities of higher layer,specifically, higher nodes, and control the connections between the userequipment (UE) 71 and the eNB 76 and the Home-eNB 75 being basestations. The MME units 73 configure an EPC being a core network. Thebase station 72 and the HeNBGW 74 configure an E-UTRAN 70.

Further, 3GPP is studying the configuration below. The X2 interfacebetween the Home-eNBs 75 is supported. In other words, the Home-eNBs 75are connected to each other by means of an X2 interface, and controlinformation is communicated between the Home-eNBs 75. The HeNBGW 74appears to the MME unit 73 as the Home-eNB 75. The HeNBGW 74 appears tothe Home-eNB 75 as the MME unit 73.

The interfaces between the Home-eNBs 75 and the MME units 73 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 75is connected to the MME unit 73 through the HeNBGW 74 and it is directlyconnected to the MME unit 73.

The base station device 72 may configure a single cell or a plurality ofcells. Each cell has a range predetermined as a coverage in which thecell can communicate with a communication terminal device and performsradio communication with the communication terminal device within thecoverage. In the case where one base station device configures aplurality of cells, every cell is configured so as to communicate withthe user equipment.

FIG. 3 is a block diagram showing the configuration of the userequipment 71 of FIG. 2 that is a user equipment according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 3 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is passed to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is converted into a baseband signal, and the basebandsignal is output to a frequency converting unit 806 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 807 to the basestation 72.

The user equipment 71 executes the reception process as follows. Theradio signal from the base station 72 is received through the antenna807. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data is passedto a decoding unit 809 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 801, and the user data is passedto the application unit 802. A series of processes by the user equipment71 is controlled by a control unit 810. This means that, though notshown in FIG. 3, the control unit 810 is connected to the individualunits 801 to 809.

FIG. 4 is a block diagram showing the configuration of the base station72 of FIG. 2 that is a base station according to the present invention.The transmission process of the base station 72 shown in FIG. 4 will bedescribed. An EPC communication unit 901 performs data transmission andreception between the base station 72 and the EPC (such as the MME unit73). HeNBGW 74, and the like. A communication with another base stationunit 902 performs data transmission and reception to and from anotherbase station. The EPC communication unit 901 and the communication withanother base station unit 902 each transmit and receive information toand from a protocol processing unit 903. The control data from theprotocol processing unit 903, and the user data and the control datafrom the EPC communication unit 901 and the communication with anotherbase station unit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is passed to anencoding unit 905 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 904 directly to a modulating unit 906 without theencoding process. The encoded data is modulated by the modulating unit906. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 907 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or aplurality of user equipments 71.

The reception process of the base station 72 is executed as follows. Aradio signal from one or a plurality of user equipments 71 is receivedthrough the antenna 908. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 907, and is then demodulated by a demodulating unit 909. Thedemodulated data is passed to a decoding unit 910 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit903, the EPC communication unit 901, or the communication with anotherbase station unit 902, and the user data is passed to the EPCcommunication unit 901 and the communication with another base stationunit 902. A series of processes by the base station 72 is controlled bya control unit 911. This means that, though not shown in FIG. 4, thecontrol unit 911 is connected to the individual units 901 to 910.

FIG. 5 is a block diagram showing the configuration of the MME accordingto the present invention. FIG. 5 shows the configuration of an MME 73 aincluded in the MME unit 73 shown in FIG. 2 described above. A PDN GWcommunication unit 1001 performs data transmission and reception betweenthe MME 73 a and the PDN GW. A base station communication unit 1002performs data transmission and reception between the MME 73 a and thebase station 72 by means of the S1 interface. In the case where the datareceived from the PDN GW is user data, the user data is passed from thePDN GW communication unit 1001 to the base station communication unit1002 via a user plane communication unit 1003 and is then transmitted toone or a plurality of base stations 72. In the case where the datareceived from the base station 72 is user data, the user data is passedfrom the base station communication unit 1002 to the PDN GWcommunication unit 1001 via the user plane communication unit 1003 andis then transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is passed from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data is passedfrom the base station communication unit 1002 to the control planecontrol unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission and receptionbetween the MME 73 a and the HeNBGW 74 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 1004 is passed from the HeNBGW communicationunit 1004 to the control plane control unit 1005. The processing resultsof the control plane control unit 1005 are transmitted to the PDN GW viathe PDN GW communication unit 1001. The processing results of thecontrol plane control unit 1005 are transmitted to one or a plurality ofbase stations 72 by means of the S1 interface via the base stationcommunication unit 1002, and are transmitted to one or a plurality ofHeNBGWs 74 via the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, and an idle state mobility managingunit 1005-3, and performs an overall process for the control plane. TheNAS security unit 1005-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 1005-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 1005-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of a paging signal in the idle state,addition, deletion, update, and search of a tracking area of one or aplurality of user equipments 71 being served thereby, and tracking arealist management.

The MME 73 a distributes a paging signal to one or a plurality of basestations 72. In addition, the MME 73 a performs mobility control of anidle state. When the user equipment is in the idle state and an activestate, the MME 73 a manages a list of tracking areas. The MME 73 abegins a paging protocol by transmitting a paging message to the cellbelonging to a tracking area in which the UE is registered. The idlestate mobility managing unit 1005-3 may manage the CSG of the Home-eNBs75 to be connected to the MME, 73 a, CSG IDs, and a whitelist.

An example of a cell search method in a mobile communication system willbe described next. FIG. 6 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a user equipment (UE) inthe LTE communication system. When starting a cell search, in Step ST1,the user equipment synchronizes slot timing and frame timing by aprimary synchronization signal (P-SS) and a secondary synchronizationsignal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which correspond one-to-one to PCIsassigned per cell, are assigned to the synchronization signals (SSs).The number of PCIs is currently studied in 504 ways. The 504 ways ofPCIs are used for synchronization, and the PCIs of the synchronizedcells are detected (specified).

In Step ST2, next, the user equipment detects a cell-specific referencesignal (CRS) being a reference signal (RS) transmitted from the basestation per cell and measures the reference signal received power(RSRP). The codes corresponding one-to-one to the PCIs are used for thereference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST1, so that the RS can be detected and the RSreceived power can be measured.

In Step ST3, next, the user equipment selects the cell having the bestRS received quality, for example, the cell having the highest RSreceived power, that is, the best cell, from one or more cells that havebeen detected up to Step ST2.

In Step ST4, next, the user equipment receives the PBCH of the best celland obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas a transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and a system frame number (SFN).

In Step ST5, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information about cell selection, and scheduling information on anotherSIB (SIBk; k is an integer equal to or greater than two). In addition,the SIB1 contains a tracking area code (TAC).

In Step ST6, next, the user equipment compares the TAC of the SIB1received in Step ST5 with the TAC portion of a tracking area identity(TAI) in the tracking area list that has already been possessed by theuser equipment. The tracking area list is also referred to as a TAIlist. TAI is the identification information for identifying trackingareas and is composed of a mobile country code (MCC), a mobile networkcode (MNC), and a tracking area code (TAC). MCC is a country code. MNCis a network code. TAC is the code number of a tracking area.

If the result of the comparison of Step ST6 shows that the TAC receivedin Step ST5 is identical to the TAC included in the tracking area list,the user equipment enters an idle state operation in the cell. If thecomparison shows that the TAC received in Step ST5 is not included inthe tracking area list, the user equipment requires a core network (EPC)including MME and the like to change a tracking area through the cellfor performing tracking area update (TAU).

The device configuring a core network (hereinafter, also referred to asa “core-network-side device”) updates the tracking area list based on anidentification number (such as UE-ID) of a user equipment transmittedfrom the user equipment together with a TAU request signal. Thecore-network-side device transmits the updated tracking area list to theuser equipment. The user equipment rewrites (updates) the TAC list ofthe user equipment based on the received tracking area list. After that,the user equipment enters the idle state operation in the cell.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world. To increase spectral efficiency,thus, it is studied to downsize cells for further spatial separation.

In the conventional configuration of cells, the cell configured by aneNB has a relatively-wide-range coverage. Conventionally, cells areconfigured such that relatively-wide-range coverages of a plurality ofcells configured by a plurality of macro eNBs cover a certain area.

When cells are downsized, the cell configured by an eNB has anarrow-range coverage compared with the coverage of a cell configured bya conventional eNB. Thus, in order to cover a certain area as in theconventional case, a larger number of downsized eNBs than theconventional eNBs are required.

In the description below, a “macro cell” refers to a cell having arelatively-wide-range coverage, that is, a cell whose coverage area isrelatively wide, such as a cell configured by a conventional eNB, and a“macro eNB” refers to an eNB configuring a macro cell. A “small cell”refers to a cell having a relatively-narrow-range coverage, that is, acell whose coverage area is relatively narrow, such as a downsized cell,and a “small eNB” refers to an eNB configuring a small cell.

The macro eNB may be, for example, a “wide area base station” describedin Non-Patent Document 8.

The small eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB configuring apico cell, a femto eNB configuring a femto cell, HeNB, remote radio head(RRH), remote radio unit (RRU), remote radio equipment (RRE), or relaynode (RN). Still alternatively, the small eNB may be a “local area basestation” or “home base station” described in Non-Patent Document 8.

FIG. 7 shows the concept of the cell configuration in which macro eNBsand small eNBs coexist. The macro cell configured by a macro eNB has arelatively-wide-range coverage 1301. A small cell configured by a smalleNB has a coverage 1302 whose range is narrower than that of thecoverage 1301 of a macro eNB (macro cell).

When a plurality of eNBs coexist, the coverage of the cell configured byan eNB may be included in the coverage of the cell configured by anothereNB. In the cell configuration shown in FIG. 7, as indicated by areference “1304” or “1305”, the coverage 1302 of the small cellconfigured by a small eNB may be included in the coverage 1301 of themacro cell configured by a macro eNB.

As indicated by a reference “1305”, the coverages 1302 of a pluralityof, for example, two small cells may be included in the coverage 1301 ofone macro cell. A user equipment (UE) 1303 is included in, for example,the coverage 1302 of the small cell and performs communication via thesmall cell.

In the cell configuration shown in FIG. 7, as indicated by a reference“1306”, the coverage 1301 of the macro cell configured by a macro eNBmay overlap the coverages 1302 of the small cells configured by smalleNBs in a complicated manner.

As indicated by a reference “1307”, the coverage 1301 of the macro cellconfigured by a macro eNB may not overlap the coverages 1302 of thesmall cells configured by small eNBs.

Further, as indicated by a reference “1308”, the coverages 1302 of alarge number of small cells configured by a large number of small eNBsmay be configured in the coverage 1301 of one macro cell configured byone macro eNB.

The need for machine-type communication (MTC) that enables communicationeven without any human manipulation of a UE is increasing. The MTC isused in many types of services, for example, sensing, meter monitoring,and parcel tracking monitoring, etc.

It is assumed that the increasing need for the MTC will be followed bythe use of excessive number of MTC user equipments (MTC UEs). Thus, theMTC UEs require lower cost and longer life.

3GPP is studying a technique for reducing the cost of the MTC UEs (seeNon-Patent Document 9). The following three requirements (1) to (3) arelisted as requirements for low cost MTC (LC-MTC).

(1) Reduced bandwidth

(2) Coverage enhancement

(3) Power consumption reduction

3GPP is studying solutions for satisfying these requirements. The UEsfor LC-MTC (hereinafter may be referred to as “LC-MTC UEs”) that arelow-cost MTC terminal devices will be described below.

Conventionally, system information (SI) is broadcasted at the entiresystem bandwidth using a PDCCH and a PDSCH. However, the LC-MTC UEsrequiring reduction in a bandwidth to be supported cannot receive the SIbroadcasted at the entire system bandwidth. Thus, new methods fornotifying the LC-MTC UEs of the SI are being studied. Here, since theLC-MTC UEs requiring reduction in the bandwidth to be supported performradio communication at a bandwidth narrower than the system bandwidththat can be used by cells, they equate to narrow-bandwidth terminaldevices.

Since the SI needs to be repeatedly broadcasted, reduction in the SI tobe notified to the LC-MTC UEs is required. The SI to be reduced includesparameters except for a SIB1, a SIB2, and a SIB14 that are SIBs forinitial access (see Non-Patent Document 10). Thus, the parameters to bereduced contain system information for reselecting cells of a SIB3, aSIB4, a SIB5, and a SIB6.

However, the UEs in an RRC_Idle state need to perform a cell reselectionprocess (see Non-Patent Document 2). Furthermore, the UEs in theRRC_Idle state move between cells if they are in the same tracking area,while maintaining the RRC_Idle state without establishing an RRCconnection.

FIG. 8 is a flowchart indicating processes of a UE in the RRC_Idle stateaccording to a conventional technique. In Step ST8001, the UE in theRRC_Idle state camps on a cell A.

In Step ST8002, the UE in the RRC_Idle state that is camping on the cellA performs discontinuous reception (DRX).

In Step ST8003, the UE performs a cell reselection process.Specifically, the UE receives the system information on the cellreselection process (hereinafter may be referred to as “reselecting-cellsystem information”) that is broadcasted by the cell A, and performs thecell reselection process using the reselecting-cell system information.

In Step ST8004, the UE detects a cell X as a result of the cellreselection process.

In Step ST8005, the UE receives broadcast information of the detectedcell X, and determines whether a TAC of the SIB1 of the detected cell Xis identical to a TAC received from the cell A on which the UE has beencamping before the cell reselection process, on the basis of thereceived broadcast information. When the TAC of the SIB1 of the detectedcell X is different from the TAC received from the cell A, the UEproceeds to Step ST8006. When the TAC of the SIB1 of the detected cell Xis identical to the TAC received from the cell A, the UE proceeds toStep ST8007 while maintaining the RRC_Idle state.

In Step ST8006, the UE performs tracking area update (TAU) through thedetected cell X. After performing the TAU process, the UE returns to theRRC_Idle state and proceeds to Step ST8007.

In Step ST8007, the UE camps on the detected cell X. After the UE campson the detected cell X, it returns to Step ST8002, and performs theprocesses from Step ST8002 to Step ST8007 again at a discontinuousreception period of the detected cell X.

If the SI to be notified to the LC-MTC UEs has been reduced and theLC-MTC UEs cannot obtain the system information for reselecting thecells, a problem in that the UE in the RRC_Idle state cannot perform thecell reselection process occurs.

When the UE cannot perform the cell reselection process and thereception quality of a serving cell on which the UE is camping hasdecreased, a problem in that the UE moves out of a coverage area occurs.

Furthermore, when the UE moves from the RRC_Idle state to theout-of-coverage area, a problem in that the UE cannot receive a pagingmessage occurs through resetting of a configuration of, for example, thediscontinuous reception (DRX) period.

The first embodiment will disclose a method for solving these problems.Upon completion of a discontinuous-reception-period timer (hereinaftermay be referred to as a “discontinuous reception timer”), the LC-MTC UEsynchronizes with a serving cell, and performs an operation fordetecting a paging message. Even when moving out of the coverage area,the LC-MTC UE sets the discontinuous reception timer active. In otherwords, the LC-MTC UE maintains the discontinuous reception timer. Astate in which the LC-MTC UE maintains the discontinuous reception timerwhile being out of the coverage area may be a new state. Alternatively,such a state may be one of the RRC_Idle states.

The LC-MTC UE does not have to receive the system information forreselecting a cell from a cell. The cell does not have to notify theLC-MTC UE of the system information for reselecting a cell. The LC-MTCUE does not have to perform the cell reselection process in the RRC_Idlestate.

Accordingly, the LC-MTC UE can perform discontinuous reception evenwithout the system information for reselecting a cell, and receive thepaging message.

FIG. 9 is an example flowchart indicating processes of the LC-MTC UE inthe RRC_Idle state according to the first embodiment.

In Step ST9001, the LC-MTC UE in the RRC_Idle state camps on, forexample, the cell A.

In Step ST9002, the LC-MTC UE in the RRC. Idle state that is camping onthe cell A performs discontinuous reception. The LC-MTC UE neitherreceives the system information for reselecting a cell from the cell Anor performs the cell reselection process.

In Step ST9003, the LC-MTC UE determines a reception condition of asignal transmitted from the cell A on which the LC-MTC UE is camping.Specifically, the LC-MTC UE determines whether the reception quality ofthe cell is not degraded and it is capable of reception. When it isdetermined to be capable of reception, the LC-MTC UE returns to StepST9002 and continues discontinuous reception. When it is determined notto be capable of reception, that is, when it is determined to beincapable of reception, the LC-MTC UE proceeds to Step ST9004 bydetermining that a predetermined moving condition is satisfied.

In Step ST9004, the LC-MTC UE moves out of the coverage area. When, forexample, the reception quality of the serving cell is lower than orequal to a predetermined threshold, it may be determined that the LC-MTCUE moves out of the coverage area as a criterion for the determination.

The predetermined threshold may be statically predetermined, forexample, in a standard, newly created and broadcasted by a cell as aparameter for the SI of the LC-MTC UE, or notified by a cell separatelyto the LC-MTC UEs through RRC signaling. The predetermined threshold maybe determined according to the terminal capability of the LC-MTC UE.

Even when being out of the coverage area, the LC-MTC UE maintains thediscontinuous reception (DRX) timer. Even when being out of the coveragearea, the LC-MTC UE can determine the discontinuous reception timing bymaintaining at least the discontinuous reception timer.

In Step ST9005, the LC-MTC UE determines whether the discontinuousreception timer has been completed. When it is determined that thediscontinuous reception timer has not been completed, that is, thediscontinuous reception timer has been incomplete, the process of StepST9005 will be performed until the discontinuous reception timer iscompleted. When it is determined that the discontinuous reception timerhas been completed, the processes return to Step ST9002, the LC-MTC UEsynchronizes with the cell A on which the LC-MTC UE has been campingbefore moving out of the coverage area, and performs discontinuousreception.

The LC-MTC UE may hold information for synchronization with a cell onwhich the LC-MTC UE has been camping before moving out of the coveragearea, and the system information received from the cell. Examples of theinformation for synchronization include a cell identifier.

The flowchart in FIG. 9 shows that the LC-MTC UE synchronizes with thecell on which the LC-MTC UE has been camping and performs discontinuousreception when it is determined that the discontinuous reception timerhas been completed. Thus, the discontinuous reception timer may be setin consideration of a time necessary to start the discontinuousreception, for example, a time necessary for the synchronization. Thediscontinuous reception timer may be set, for example, to a time earlierthan a time at which one discontinuous reception period has elapsed orto a time shorter than the discontinuous reception period.

Since the LC-MTC UE according to the first embodiment does not performthe cell reselection process, it moves out of the coverage area when thereception quality of a serving cell, for example, the reception qualityof a reference signal (RS) of a cell such as reference signal receivedpower (RSRP) and reference signal received quality (RSRQ) is degraded.

When the UE moves out of the coverage area, conventionally, it leavesthe RRC_Idle state and resets the configuration for the cell on whichthe UE has been camping. Thus, the discontinuous reception timer is alsoreset.

However, the discontinuous reception timer is maintained even when theUE moves out of the coverage area according to the first embodiment.Accordingly, even when the UE temporarily moves out of the coveragearea, it can perform discontinuous reception again with the cell onwhich the UE has been camping, using the discontinuous reception timer.Since the cell notifies the LC-MTC UE of a paging message in thediscontinuous reception period if the paging message exists, the LC-MTCUE can receive the paging message notified from the cell.

With the method disclosed in the first embodiment, the LC-MTC UE canmaintain the RRC_Idle state even without the information for reselectinga cell. Thus, the LC-MTC UE can receive the paging message. Accordingly,the LC-MTC UE can receive a command and data that are notified from, forexample, an MTC operator or an MTC server, etc.

Furthermore, since the cell does not have to broadcast the informationfor reselecting a cell to the LC-MTC UE, it is possible to reduce anamount of the SI to be broadcasted. Furthermore, since the LC-MTC UEdoes not perform a cell reselection process and a cell selectionprocess, the power consumption thereof can be reduced. Furthermore,since the number of processes can be reduced, the structure issimplified and a malfunction of the system can be reduced.

Although provision of a state of maintaining the discontinuous receptiontimer in an out-of-coverage area, that is, provision of one of theRRC_Idle states is disclosed, the process of moving to the conventionalout-of-coverage area cannot be performed.

Here, the process of moving to the conventional out-of-coverage area maybe newly provided. When the LC-MTC UE fails discontinuous reception apredetermined number of times, it moves to the conventionalout-of-coverage area. When the LC-MTC UE can neither synchronize with acell nor receive a control signal or a control channel with thediscontinuous reception timing, it may be determined that thediscontinuous reception has failed. A failure in the discontinuousreception may be a case where the LC-MTC UE cannot receive any signaldue to degradation in the reception quality in Step ST9003 in FIG. 9.

The predetermined number of times of failure may be a case where theLC-MTC UE consecutively fails discontinuous reception for apredetermined number of times or a case where the LC-MTC UE failsdiscontinuous reception a predetermined number of times over apredetermined period of time. The information necessary for the LC-MTCUE to move to the conventional out-of-coverage area such as thepredetermined number of times and the predetermined period may bepredetermined, for example, in a standard or broadcasted as the SI forthe LC-MTC UE. Alternatively, the information may be notified by thecell upon establishment of the RRC connection in the initial access.

Accordingly, the LC-MTC UE does not permanently continue the state ofmaintaining the discontinuous reception timer and repeating thediscontinuous reception. Thus, the power consumption of the LC-MTC UEcan be reduced.

First Modification of First Embodiment

A first modification will disclose another method for solving theproblems described in the first embodiment. The LC-MTC UE performs thecell selection process when moving out of the coverage area. Examples oftriggers for starting the cell selection process may include a time whenthe LC-MTC UE moves out of the coverage area and a time when thediscontinuous reception timer has been completed after the LC-MTC UEmoves out of the coverage area.

The LC-MTC UE does not have to receive the system information forreselecting a cell from a cell. The cell does not have to notify theLC-MTC UE of the system information fir reselecting a cell. The LC-MTCUE does not have to perform the cell reselection process in RRC_Idle.

Accordingly, the LC-MTC UE can perform discontinuous reception andreceive a paging message even without the information for reselecting acell.

In the case where the time when the LC-MTC UE moves out of the coveragearea is a trigger for starting the cell selection process, the cellselection process can be promptly performed. Accordingly, a favorablecell can be promptly detected and communication with the favorable cellcan be promptly performed, according to variations in radio propagationenvironment.

In the case where the time when the discontinuous reception timer hasbeen completed is a trigger for starting the cell selection process, acell cannot be promptly detected and a delay may occur because celldetection is performed in accordance with the discontinuous receptionperiod. However, when the cell on which the LC-MTC UE has been campingbefore moving out of the coverage area is selected in the cell selectionprocess, it is possible to avoid wasteful reception. Thus, the powerconsumption of the LC-MTC UE can be reduced.

In the case where the time when the discontinuous reception timer hasbeen completed is a trigger for starting the cell selection process, theLC-MTC UE may maintain the discontinuous reception timer in moving outof the coverage area. A state in which the discontinuous reception timeris maintained in the out-of-coverage area may be a new state.Alternatively, such a state may be one of the RRC_Idle states.

The LC-MTC UE may not necessarily perform an RRC connectionestablishment process when it selects a cell in the cell selectionprocess.

After the cell is selected, when the selected cell belongs to the sameTA as that of a cell before the selection, the LC-MTC UE enters theRRC_Idle state according to the broadcast information of the selectedcell without the RRC connection establishment process.

After the cell is selected, when the selected cell does not belong tothe same TA as that of the cell before the selection, the LC-MTC UEperforms the RRC connection establishment process and the TAU.

Accordingly, since the RRC connection establishment process afterselecting the cell can be omitted as necessary, the power consumption ofthe LC-MTC UE can be reduced.

Although it is disclosed that the LC-MTC UE may not necessarily performthe RRC connection establishment process when a cell is selected in thecell selection process, the LC-MTC UE may perform a periodic TAU. TheRRC connection establishment process for the periodic TAU may beperformed. Accordingly, a core network side can perform mobilitymanagement of the LC-MTC UE.

When a cell cannot be selected through the cell selection process, theLC-MTC UE moves to the conventional out-of-coverage area.

The process of moving to the conventional out-of-coverage area asdisclosed in the first embodiment may be applied. When the LC-MTC UEperforms the cell selection process instead of the discontinuousreception and fails the cell selection process a predetermined number oftimes, it may move to the conventional out-of-coverage area.Accordingly, when the radio propagation environment temporarily worsens,a cell can be selected.

FIG. 10 is an example flowchart indicating processes of the LC-MTC UE inRRC_Idle according to the first modification of the first embodiment.Since the flowchart of FIG. 10 is similar to the flowchart of FIG. 9 asdescribed above, the same step numbers will be assigned to the sameSteps and the common description thereof will be omitted.

FIG. 10 shows an example in that completion of the discontinuousreception timer is a trigger for starting the cell selection process.Even when moving out of the coverage area, the LC-MTC UE maintains thediscontinuous reception timer.

In Step ST9005 after Steps ST9001 to ST9004, the LC-MTC UE determineswhether the discontinuous reception timer has been completed. When thediscontinuous reception timer has not been completed yet, the process ofStep ST9005 will be performed until the discontinuous reception timer iscompleted. When the discontinuous reception timer has been completed,the processes proceed to Step ST1001.

In Step ST1001, the LC-MTC UE starts the cell selection process.

In Step ST1002, the LC-MTC UE selects the cell X through the cellselection process.

In Step ST1003, it is determined whether the selected cell X is a cellon which the LC-MTC UE has been camping before moving out of thecoverage area. When it is determined in Step ST1003 that the selectedcell X is the cell on which the LC-MTC UE has been camping before movingout of the coverage area, the processes return to Step ST9002 and thediscontinuous reception is performed. Since the discontinuous receptiontimer is set active in the cell on which the LC-MTC UE has been campingbefore moving out of the coverage area, after it is determined that thediscontinuous reception timer has been completed, the discontinuousreception can be immediately performed with the cell.

When the selected cell X is the cell on which the LC-MTC UE has beencamping before moving out of the coverage area, the processes from StepsST1004 to ST1006 that are processes after the LC-MTC UE selects the cellcan be omitted. Thus, the power consumption of the LC-MTC UE can bereduced.

When it is determined in Step ST1003 that the selected cell X is not thecell on which the LC-MTC UE has been camping before moving out of thecoverage area, the processes proceed to Step ST1004.

In Step ST1004, the UE receives broadcast information of the selectedcell X, and determines whether the TAC of the SIB1 of the selected cellX is identical to the TAC received from the cell A on which the UE has,been camping before moving out of the coverage area, on the basis of thereceived broadcast information. When the TAC of the SIB1 of the selectedcell X is different from the TAC received from the cell A, the processesproceed to Step ST1005. When the TAC of the SIB1 of the selected cell Xis identical to the TAC received from the cell A, the UE proceeds toStep ST1006 while maintaining the RRC_Idle state.

In Step ST1005, the UE performs the TAU through the selected cell X.After performing the TAU process, the UE returns to the RRC_Idle stateand proceeds to Step ST1006.

In Step ST1006, the UE camps on the selected cell X. After the UE campson the selected cell X, it returns to Step ST9002 at the discontinuousreception period of the selected cell X, and performs the processes fromStep ST9002 to Step ST1006 again.

When a cell cannot be selected through the cell selection process inStep ST1002, the UE moves to the conventional out-of-coverage area.

When the cell on which the UE has been camping before moving out of thecoverage area is selected through the cell selection process in StepST1002, the processes may proceed to Step ST1004 without proceeding tothe discontinuous reception in Step ST9002. The determining process inStep ST1003 may be omitted.

When the cell on which the UE has been camping before moving out of thecoverage area is selected, the discontinuous reception cannot beimmediately performed. However, since the process in Step ST1003 can beomitted, the control can be simplified.

The LC-MTC UE may hold information for synchronization with the cell onwhich the LC-MTC UE has been camping before moving out of the coveragearea, and the system information received from the cell. Examples of theinformation for synchronization include a cell identifier.

In the case where the time when the discontinuous reception timer hasbeen completed is a trigger for starting the cell selection process, thediscontinuous reception timer may be set in consideration of a timenecessary to start the discontinuous reception, for example, a timenecessary for the cell selection process. The discontinuous receptiontimer may be set, for example, to a time earlier than a time at whichone discontinuous reception period has elapsed or to a time shorter thanthe discontinuous reception period.

The method disclosed in the first modification can produce the sameadvantages as described in the first embodiment. Furthermore, since thecell reselection process is not performed, the power consumption of theLC-MTC UE can be reduced. Furthermore, since the number of processes canbe reduced, the structure is simplified and a malfunction of the systemcan be reduced.

When a cell is temporarily selected in the initial access, the servingcell will not be changed from then on in the method disclosed in thefirst embodiment. In contrast, since the cell selection process isstarted when the LC-MTC UE moves out of the coverage area according tothe first modification, the serving cell can be changed.

Accordingly, even when the radio propagation environment of the cell onwhich the LC-MTC UE has been camping before moving out of the coveragearea is degraded, a new cell can be selected. Thus, a stablecommunication system can be built.

A new discontinuous reception timer may be set as the discontinuousreception timer. The discontinuous reception timer is enabled whilebeing maintained in the out-of-coverage area.

The new discontinuous reception timer may be used in common in a system,in MTC, or among the LC-MTC UEs, or provided for each cell.Alternatively, the new discontinuous reception timer may be used incommon in a predetermined group. Alternatively, the new discontinuousreception timer may be provided for each of the LC-MTC UEs.

The following five examples (1) to (5) will be disclosed as specificexamples of methods for recognizing the new discontinuous receptiontimer by the LC-MTC UE.

(1) The new discontinuous reception timer is statically predetermined,for example, in a standard. The method is effective when the newdiscontinuous reception timer is used in common in a system or among theLC-MTC UEs. Accordingly, an amount of information to be notified fromthe cell to the LC-MTC UE can be reduced.

(2) The new discontinuous reception timer is notified by an MIB. Themethod is effective when the new discontinuous reception timer isprovided for each cell. Since the MIB is notified by six resource blocks(6 RBs) at the center of the system bandwidth, even the LC-MTC UE inwhich the bandwidth has been reduced can receive the new receptiontimer.

(3) The new discontinuous reception timer is notified by the S1 for theLC-MTC UE. The method is effective when the new discontinuous receptiontimer is provided for each cell or each of the LC-MTC UEs. The newdiscontinuous reception timer can be received irrespective of an RRCstate (RRC_Idle, RRC_Connected) of the LC-MTC UE.

(4) The new discontinuous reception timer is notified by RRC signaling.Here, the new discontinuous reception timer may be notified in theinitial access. The method may be applied when the new discontinuousreception timer is provided for each cell or each of the LC-MTC UEs. Alarger amount of parameters can be notified than that when the newdiscontinuous reception timer is notified by the MIB or the SI.Conversely, the amount of information to be notified by the MIB or theSI can be reduced.

(5) Timer values are statically predetermined, for example, in astandard to provide indications corresponding to the respective timervalues. The MIB or the SI for the LC-MTC UE with the indications may benotified to the LC-MTC UE. The method is effective when the newdiscontinuous reception timer is provided for each cell or each of theLC-MTC UEs. Thus, the amount of information in the MIB or the SI can bereduced.

Second Modification of First Embodiment

A second modification will disclose another method for solving theproblems described in the first embodiment. The LC-MTC UE performs thecell selection process in RRC_Idle. The cell selection process may beperformed before moving out of the coverage area. The cell selectionprocess may be performed instead of the conventional cell reselectionprocess.

The LC-MTC UE does not have to receive the system information forreselecting a cell from a cell. The cell does not have to notify theLC-MTC UE of the system information for reselecting a cell. The LC-MTCUE does not have to perform the cell reselection process in RRC_Idle.

Accordingly, the LC-MTC UE can perform discontinuous reception andreceive a paging message even without the information for reselecting acell.

Since there is no criterion for the cell selection process in RRC_Idle,criteria for the cell selection process are established in the secondmodification. Particularly, a criterion for starting the cell selectionprocess in RRC_Idle is established. Specifically, a parameter for thecriterion for starting the cell selection process is defined. A cellnotifies the LC-MTC UE of the parameter for the criterion. Examples ofthe parameter for the criterion include a period for measuring thereception quality of a serving cell, a measurement filter coefficient,and a threshold, etc.

Only a threshold for the reception quality may be provided as theparameter for the criterion. The period for measuring the receptionquality and the measurement filter coefficient may be compliant with theconventional cell selection process. Setting only the threshold for thereception quality enables reduction in the amount of information to benotified from the cell to the LC-MTC UE. When the threshold for thereception quality is set and the reception quality of the serving cellis lower than the threshold for the cell selection process, the LC-MTCUE may start to select a cell.

Accordingly, the LC-MTC UE can start the cell selection process inRRC_Idle.

The threshold for starting the cell selection process may be higher thanthe value of the reception quality for moving to the conventionalout-of-coverage area. Alternatively, the threshold may be higher thanthe reception quality for moving out of the coverage area or a thresholdfor moving out of the coverage area which is disclosed in the firstembodiment or in the first modification of the first embodiment.Accordingly, the LC-MTC UE can start the cell selection process beforemoving out of the coverage area.

Conventionally, the cell reselection process has been started using thesystem information for the cell reselection process. However, the LC-MTCUE that cannot obtain the system information for the cell reselectionprocess cannot perform the cell reselection process. Thus, the LC-MTC UEmay perform the cell selection process.

However, the cell selection process has been conventionally started by anon-access stratum (NAS). Since determination by the NAS is necessary inRRC_Idle, the processes become complicated. Thus, the LC-MTC UE mayperform the cell selection process without requiring an instruction ofthe NAS in RRC_Idle. The LC-MTC UE may perform the cell selectionprocess through determination by an access stratum (AS) in RRC_Idle.

The parameter for the criterion for starting the cell selection processin RRC_Idle may be used in common in a system, in MTC, or among theLC-MTC UEs, or provided for each cell. Alternatively, the parameter forthe criterion may be used in common in a predetermined group.Alternatively, the parameter for the criterion may be provided for eachof the LC-MTC UEs. Furthermore, the parameter for the criterion may beobtained by combination of these.

The following five examples (1) to (5) will be disclosed as specificexamples of methods for recognizing the parameter for the criterion bythe LC-MTC UE.

(1) The parameter is statically predetermined, for example, in astandard. The method is effective when the parameter is used in commonin a system or among the LC-MTC UEs. Accordingly, an amount ofinformation to be notified from the cell to the LC-MTC UE can bereduced.

(2) The parameter is notified by an MIB. The method is effective whenthe parameter is provided for each cell. Since the MIB is notified bysix resource blocks at the center of the system bandwidth, even theLC-MTC UE in which the bandwidth has been reduced can receive theparameter.

(3) The parameter is notified by the SI for the LC-MTC UTE. The methodis effective when the parameter is provided for each cell or each of theLC-MTC UEs. The parameter can be received irrespective of an RRC state(RRC_Idle, RRC_Connected) of the LC-MTC UE.

(4) The parameter is notified by RRC signaling. Here, the parameter maybe notified in the initial access. The method may be applied when theparameter is provided for each cell or each of the LC-MTC UEs. A largeramount of parameters can be notified than that when the parameter isnotified by the MIB or the SI. Conversely, the amount of information tobe notified by the MIB or the SI can be reduced.

(5) Parameter groups are statically predetermined, for example, in astandard to provide indications corresponding to the respectiveparameter groups. The MIB or the SI for the LC-MTC UE with theindications may be notified to the LC-MTC UE. The method is effectivewhen the parameter is provided for each cell or each of the LC-MTC UEs.Thus, the amount of information in the MIB or the SI can be reduced.

FIG. 11 is an example flowchart indicating processes of the LC-MTC UE inRRC_Idle according to the second modification of the first embodiment.Since the flowchart of FIG. 11 is similar to the flowchart of FIG. 10,the same step numbers will be assigned to the same Steps and the commondescription thereof will be omitted.

In Step ST1101, the LC-MTC UE receives a threshold for starting the cellselection process (hereinafter may be referred to as “cell selectionstarting threshold”) from the cell A.

In Step ST9001, the LC-MTC UE in the RRC_Idle state camps on the cell A.In the example of FIG. 11, the cell A notifies the LC-MTC UE of the cellselection starting threshold as system information for the LC-MTC UE.

In Step ST9002, the LC-MTC UE that is camping on the cell A performsdiscontinuous reception.

In Step ST1102, the LC-MTC UE determines, using the cell selectionstarting threshold received from the cell A, whether the receptionquality of the serving cell is lower than the cell selection startingthreshold. When it is determined that the reception quality of theserving cell is lower than the cell selection starting threshold, theprocesses proceed to Step ST1001. When it is determined that thereception quality of the serving cell is not lower than the cellselection starting threshold, the processes return to Step ST9002 andthe discontinuous reception operation is performed.

In Step ST1001, the cell selection process is started. In Step ST1002,the LC-MTC UE selects the cell X through the cell selection process.

In Step ST1103, the UE receives the system information notified from theselected cell X. This system information includes the cell selectionstarting threshold for starting the cell selection process of the cellX. In other words, the UE receives the cell selection starting thresholdby receiving the system information from the selected cell X.

The LC-MTC UE that has received the cell selection starting threshold ofthe cell X in Step ST1103 determines in Step ST1004 whether the TAC ofthe SIB1 of the selected cell X is identical to the TAC received fromthe cell A on which the LC-MTC UE has been camping until just before,that is, the cell A on which the LC-MTC UE has been camping beforemoving out of the coverage area. When the TAC of the SIB1 of theselected cell X is different from the TAC received from the cell A, theprocesses proceed to Step ST1005. When the TAC of the SIB1 of theselected cell X is identical to the TAC received from the cell A, the UEproceeds to Step ST1006 while maintaining the RRC_Idle state.

In Step ST1005, the UE performs the TAU through the selected cell X.After performing the TAU process, the UE returns to the RRC_Idle stateand proceeds to Step ST1006.

In Step ST1006, the UE camps on the selected cell X. After the FE campson the cell X, it returns to Step ST9002 at the discontinuous receptionperiod of the selected cell X, and performs the processes from StepST9002 to Step ST1006 again.

Accordingly, the LC-MTC UE can perform the cell selection process inRRC_Idle. The cell selection process enables selection of a cell withsuperior reception quality. With the cell selection process, a state inwhich the LC-MTC UE in the RRC_Idle state moves out of the coverage areacan be eliminated as much as possible.

Thus, even when change in the radio propagation environment prolongs theworse reception quality of the serving cell, another cell can beselected and communication can be performed through the cell.Accordingly, a stable communication system can be built.

The LC-MTC UE maintains the RRC. Idle state when selecting a cell. Theconfiguration in RRC_Idle is maintained. The LC-MTC UE may notnecessarily perform the RRC connection establishment process when a cellis selected in the cell selection process.

After the cell is selected, when the selected cell belongs to the sameTA as that of the cell before the selection, the RRC_Idle state ismaintained according to the broadcast information of the selected cellwithout the RRC connection establishment process.

After the cell is selected, when the selected cell does not belong tothe same TA as that of the cell before the selection, the RRC connectionestablishment process and the TAU are performed.

Accordingly, since the RRC connection establishment process afterselecting the cell can be omitted as necessary, the power consumption ofthe LC-MTC UE can be reduced.

The LC-MTC UE moves to the conventional out-of-coverage area when a cellcannot be selected through the cell selection process. The process ofmoving to the conventional out-of-coverage area as disclosed in thefirst embodiment may be applied. When the LC-MTC UE performs the cellselection process instead of the discontinuous reception and fails thecell selection process a predetermined number of times, it may move tothe conventional out-of-coverage area. Accordingly, when the radiopropagation environment temporarily worsens, a cell can be selected.

The other methods for triggering the start of the cell selection processmay include predetermined timing and periodical execution. The LC-MTC UEperforms the cell selection process at a predetermined period or withpredetermined timing. The predetermined period may be asynchronous tothe discontinuous reception period, or an integer multiple or anintegral submultiple of the discontinuous reception period. Accordingly,start of the cell selection process can be set separately from thediscontinuous reception period. Accordingly, the cell selection processcan be flexibly started according to an installation environment and anoperational environment of the LC-MTC UE.

The method on the new discontinuous reception timer disclosed in thefirst modification of the first embodiment may be applied to a methodfor setting predetermined timing or a predetermined period. Acombination of predetermined timing or a predetermined period with athreshold may be used as a trigger for starting the cell selectionprocess. Accordingly, the cell selection process can be more flexiblystarted according to the installation environment, the operationalenvironment, and the radio propagation environment of the LC-MTC UE.

Third Modification of First Embodiment

A third modification will disclose another method for solving theproblems described in the first embodiment. The LC-MTC UE performs thecell reselection process in RRC_Idle. The problem here is how the LC-MTCUE recognizes a parameter necessary for the cell reselection process(hereinafter may be referred to as a “cell reselection processparameter”). A method for configuring a cell reselection processparameter of the LC-MTC UE and a method for recognizing the cellreselection process parameter by the LC-MTC UE will be disclosed.

The cell reselection process parameter of the LC-MTC UE may be used incommon in a system, in MTC, or among the LC-MTC UEs, or provided foreach cell. The cell reselection process parameter may be used in commonin a predetermined group. Alternatively, the cell reselection processparameter may be provided for each of the LC-MTC UEs. Furthermore, thecell reselection process parameter may be obtained by combination ofthese.

The following five examples (1) to (5) will be disclosed as specificexamples of methods for recognizing the cell reselection processparameter by the LC-MTC UE.

(1) The parameter is statically predetermined, for example, in astandard. The method is effective when the parameter is used in commonin a system or among the LC-MTC UEs. Accordingly, an amount ofinformation to be notified from the cell to the LC-MTC UE can bereduced.

(2) The parameter is notified by an MIB. The method is effective whenthe parameter is provided for each cell. Since the MIB is notified bysix resource blocks at the center of the system bandwidth, even theLC-MTC UE in which the bandwidth has been reduced can receive theparameter.

(3) The parameter is notified by the SI for the LC-MTC UE. The method iseffective when the parameter is provided for each cell or each of theLC-MTC UEs. The parameter can be received irrespective of an RRC state(RRC_Idle, RRC_Connected) of the LC-MTC UE.

(4) The parameter is notified by RRC signaling. Here, the parameter maybe notified in the initial access. The method may be applied when theparameter is provided for each cell or each of the LC-MTC UEs. A largeramount of parameters can be notified than that when the parameter isnotified by the MIB or the SI. Conversely, the amount of information tobe notified by the MIB or the SI can be reduced.

(5) Parameter groups for cell reselection process are staticallypredetermined, for example, in a standard to provide indicationscorresponding to the respective groups. The MIB or the SI for the LC-MTCUE with the indications may be notified to the LC-MTC UE. The method iseffective when the parameter is provided for each cell or each of theLC-MTC UEs. Thus, the amount of information in the MIB or the SI can bereduced.

The method above may be applied to every parameter or every parametergroup. The cell reselection process parameter of the LC-MTC UE may beused in common among cells in a TA. Alternatively, the cell reselectionprocess parameter of the LC-MTC UE may be used in common in MTC or in apredetermined group of the LC-MTC UEs.

Accordingly, when the cell reselection process parameter is notified byRRC signaling in the specific example of (4), the LC-MTC UE reselectscells in RRC_Idle and selects a cell in the same TA, the LC-MTC UE cancontinue to use the cell reselection process parameter. When the LC-MTCUE selects the cell in the same TA, it does not have to establish theRRC connection with the cell.

Thus, the LC-MTC UE can continue to perform the cell reselectionprocess. Furthermore, notification of the parameter by RRC signaling inthe specific example of (4) enables reduction in the amount ofinformation to be notified by the MIB or the SI.

The RRC connection may be certainly established when the LC-MTC UEchanges a cell as an alternative method. The notification method by RRCsignaling in the specific example of (4) may be applied thereto.Accordingly, even when the LC-MTC UE reselects cells in RRC_Idle andselects a cell in the same TA, it can obtain a cell reselectionparameter for the cell by RRC signaling through establishment of the RRCconnection.

When it is necessary to notify the LC-MTC UE of not only the cellreselection parameter but also the system information by RRC signaling,in the case where the LC-MTC UE changes the cell, it may establish theRRC connection. The system information may be notified to the LC-MTC UEduring the RRC connection.

Fourth Modification of First Embodiment

The first embodiment has disclosed that the reduction in the SI to benotified to the LC-MTC UEs is required and the SI to be reduced includesparameters except for a SIB1, a SIB2, and a SIB14 that are SIBs forinitial access.

The fourth modification will disclose another method for reducing theSI. The SI fir the cell reselection process that is included in theconventional SI is partly reduced. The conventional SI for the cellreselection process is partly reduced to the SI for the cell reselectionprocess of the LC-MTC UE. A cell notifies the LC-MTC UE of the SI forcell reselection process of the LC-MTC UE.

The following (1) to (7) will be disclosed as example parameters to bereduced among the conventional cell reselection parameters.

(1) Parameters on speed, for example, “speedStateReselectionPars” andparameters included in “speedStateReselectionPars”, etc.; the LC-MTC UEthat moves within a predetermined cell or does not move does not needthe parameters on speed. Thus, even when the parameters on speed arereduced, the LC-MTC UE can perform the cell reselection process.

(2) Parameters on inter-frequency, for example,“cellReselectionServingFreqInfo” and parameters included in“cellReselectionServingFreqInfo”, and the SIB5 and parameters includedin the SIB5, etc.; the LC-MTC UE that operates at a predeterminedcarrier frequency does not need the parameters on inter-frequency. Thus,even when the parameters on inter-frequency are reduced, the LC-MTC UEcan perform the cell reselection process.

(3) Parameters on inter radio access technology (inter-RAT), forexample, “cellReselectionServingFreqInfo” and parameters included in“cellReselectionServingFreqInfo”, and the SIB6 and parameters includedin the SIB6, etc.; the LC-MTC UE that operates under predetermined RATdoes not need the parameters on inter-RAT. Thus, even when theparameters on inter-RAT are reduced, the LC-MTC UE can perform the cellreselection process.

(4) Parameters on priority, for example, “cellReselectionPriority”,etc.; the LC-MTC UE that operates at a predetermined carrier frequencydoes not need the parameters on priority. Thus, even when the parameterson priority are reduced, the LC-MTC UE can perform the cell reselectionprocess.

(5) Parameters on measurement bandwidth, for example, “q-QualMinWB”,etc.; the measurement bandwidth for the LC-MTC UE that operates at areduced bandwidth may be determined in advance as the reduced bandwidth.Here, the parameters on measurement bandwidth are unnecessary. Thus,even when the parameters on measurement bandwidth are reduced, theLC-MTC UE can perform the cell reselection process.

(6) Parameters on RSRQ, for example, “s-IntraSearchQ” and “q-QualMinWB”,etc.; the LC-MTC UE may predetermine the reception quality as RSRP.Here, the parameters on RSRQ are unnecessary. Thus, even when theparameters on the RSRQ are reduced, the LC-MTC UE can perform the cellreselection process.

(7) A part or the entire of the parameters (1) to (6) may hold.

The following six examples (1) to (6) will be disclosed as exampleparameters that are not to be reduced among the conventional cellreselection parameters.

(1) Parameters on start of the cell reselection process, for example,“s-IntraSearchP” and “s-IntraSearchQ”, etc.; the parameters on start ofthe cell reselection process are parameters necessary for starting thecell re election process. Retaining the parameters on start of the cellreselection process enables the LC-MTC UE to start the cell reselectionprocess.

(2) Parameters on measurement of a cell in the cell reselection process,for example, “t-ReselectionEUTRA”, etc.; the parameters on measurementof the cell in the cell reselection process are parameters necessary formeasuring the reception quality of the cell in the cell reselectionprocess. Retaining the parameters on measurement of the cell in the cellreselection process enables the LC-MTC UE to recognize how to measurethe cell.

(3) Parameters on selection of a cell in the cell reselection process,for example, “q-Hyst”, etc.; the parameters on selection of the cell inthe cell reselection process are parameters necessary for fulfilling thecriterion fir reselecting a cell. Retaining the parameters on selectionof the cell in the cell reselection process enables the LC-MTC UE torecognize how to select a cell.

(4) Parameters on intra-frequency, for example, the SIB3 and parametersincluded in the SIB3, etc.; the parameters on intra-frequency areparameters necessary for the LC-MTC UE that operates at a predeterminedcarrier frequency. Retaining the parameters on intra-frequency enablesthe LC-MTC UE to perform a cell reselection process on a cell at theintra-frequency.

(5) Parameters on particular cell lists, for example,“intraFreqNeighCellList”, “intraFreqBlackCellList”, and“csg-PhysCellIdRange”, etc.; the parameters on particular cell lists areparameters indicating whether a cell reselection can be performed on apredetermined cell. Furthermore, the parameters on particular cell listsare parameters necessary for the LC-MTC UE that operates in apredetermined cell. Retaining the parameters on particular cell listsenables the LC-MTC UE to perform the cell reselection process on thepredetermined cell.

(6) A part or the entire of the parameters (1) to (5) may hold.

When the conventional SI for the cell reselection process is partlyreduced to the SI for the cell reselection process of the LC-MTC UE, allthe parameters necessary for the criteria for the cell reselectionprocess cannot be obtained. Here, criteria for the cell reselectionprocess in which the reduced parameters are not used may be newlyestablished. To put it the simplest, criteria in which the reducedparameters are omitted may be established.

For example, a case where the SI for the cell reselection process of theLC-MTC UE is limited to the parameters on start of the cell reselectionprocess will be disclosed. A cell notifies the LC-MTC UE of a parameter“s-IntraSearchP” as the St. The LC-MTC UE measures the reception qualityof the serving cell, that is, the RSRP herein. When the measurementvalue is lower than or equal to the parameter “s-IntraSearchP”, the cellreselection process is started. The criteria for the cell reselectionprocess are indicated below.Rs=Qmeas,s, Rn=Qmeas,n

A cell with the highest reception quality is selected from among Rs andRn. Here, Qmeas, s is a measurement value of the reception quality ofthe serving cell, and Qmeas, n is a measurement value of the receptionquality of the adjacent cell.

The method disclosed in the third modification of the first embodimentmay be applied to a method for recognizing, by the LC-MTC UE, the SI forthe cell reselection process of the LC-MTC UE that is obtained by partlyreducing the conventional SI for the cell reselection process.

Accordingly, even when the conventional SI for the cell reselectionprocess is partly reduced to the SI for the cell reselection process ofthe LC-MTC UE, the cell reselection process can be performed. The cellreselection can be more flexibly started according to the installationenvironment, the operational environment, and the radio propagationenvironment of the LC-MTC UE. With the cell reselection process, a statein which the LC-MTC UE in the RRC_Idle state moves out of the coveragearea can be eliminated as much as possible. Furthermore, partialreduction of the SI enables reduction in necessary resources even whenthe SI is repeatedly notified.

Second Embodiment

The LC-MTC UE may select a far cell depending on a radio environment inthe cell selection process. As described in the first embodiment, whenthe SI for reselecting a cell is reduced to meet the demand forreduction in the SI of the LC-MTC UE, unless something is done, the cellreselection process of the LC-MTC UE is not performed.

Here, until the next cell selection process is performed, it isnecessary to camp on the far cell that has been temporarily selected.Accordingly, it is highly probable that the reception quality in theLC-MTC UE is degraded and the LC-MTC UE moves out of the coverage area.When moving out of the coverage area, the LC-MTC UE newly performs acell selection process according to an instruction of the NAS,establishes the RRC connection, and performs an attach process or theTAU process. Accordingly, a problem with increase in power consumptionof the LC-MTC UE occurs.

The cell selection process has a stored information cell selectionfunction (see Non-Patent Document 2). Even with this function, when afar cell is initially selected and no cell reselection process isperformed, information on the first far cell is merely stored and thefar cell is then selected in the following cell selection processes.Thus, even with the stored information cell selection function, aproblem with increase in power consumption of the UE occurs.

The second embodiment will disclose a method for solving these problems.Priorities are assigned in the cell selection process.

The following three examples (1) to (3) will be disclosed as examples ofinformation to which the priorities are assigned.

(1) Carrier frequency information; the information may be indicated byan absolute radio-frequency channel number (ARFCN).

(2) Cell information; the information may be a cell identifier or a PCI.

(3) A combination of (1) and (2) above

The information may be set with a priority. Accordingly, carrierinformation or cell information for selecting a cell in priority can berecognized. The priorities may be assigned in common in a system, inMTC, or among the LC-MTC UEs, or for each cell. The priorities may beassigned in common in a predetermined group. Alternatively, thepriorities may be assigned for each of the LC-MTC UEs. Furthermore, thepriorities may be assigned according to the combination above.

The method for recognizing the new discontinuous reception timer by theLC-MTC UE that is disclosed in the first modification of the firstembodiment may be applied to a method for recognizing the priorities bythe LC-MTC UE. The priorities may be stored in a SIM as an alternativemethod. The priorities may be stored for each operator to be registered.The priorities may be stored in association with UE capability.Accordingly, the LC-MTC UE can recognize the priorities in the cellselection process. The maximum number of the priorities may be set.Accordingly, the amount of information to be notified to the LC-MTC UEcan be reduced.

The following three examples (1) to (3) will be disclosed as examplesubjects to which the priorities are assigned.

(1) eNBs (cell)

(2) MMEs; here, the MMEs notify an eNB of the priority. The priority maybe notified using an S1 interface.

(3) Operators; here, the operators notify an eNB of the priority. Thepriority may be notified through an MME. Furthermore, the operators maywrite the priority in a SIM of the LC-MTC UE.

An example method for deriving the priorities will be hereinafterdisclosed. The priorities are determined according to an installationlocation of the LC-MTC UE. An eNB may obtain the installation locationof the LC-MTC UE using a location system. Alternatively, the eNB mayobtain the installation location of the LC-MTC UE using a function ofminimization of drive tests (MDT). Alternatively, an operator may obtaininformation on the installation location of the LC-MTC UE.

The installation location is determined according to a result of ameasurement report by the LC-MTC UE as an alternative method. Forexample, the eNB that has received a measurement report on the servingcell of the LC-MTC UE or on the neighbor cells averages or filters themeasurement results for a predetermined period of time. The eNB mayderive a carrier frequency or a cell having the best reception qualityfrom a result of the averaging or the filtering and assign the highestpriority to the carrier frequency or the cell. The priorities may beassigned in descending order of the reception quality.

Although the cells with the best reception quality are selected in theconventional cell selection process, the cells can be selected accordingto the priorities with the method disclosed in the second embodiment.Accordingly, even when the LC-MTC UE does not perform the cellreselection process, the power consumption of the LC-MTC UE can bereduced. Since a cell with the higher priority can be selected inperforming the cell selection process, the power consumption of theLC-MTC UE can be reduced.

First Modification of Second Embodiment

A first modification will disclose another method for solving theproblems described in the second embodiment. Cell selection candidatesare provided. One or more cell selection candidates are provided. Themethod disclosed in the second embodiment may be applied to exampleinformation for providing the cell selection candidates, a method forrecognizing the cell selection candidates by the LC-MTC UE, and asubject that determines the cell selection candidates. A predeterminednumber of the cell selection candidates may be determined in descendingorder of the priorities.

A method for deriving a cell to be selected from the cell selectioncandidates will be hereinafter disclosed. The LC-MTC UE detects cells inthe cell selection candidates in selecting a cell. Not only the carrierfrequency information or the cell information of the detected cells butalso the reception quality thereof, specifically, at least one of theRSRP and the RSRQ as the RS reception quality are stored. The LC-MTC UEassigns priorities to cells in descending order of the receptionquality, and selects the cells in the descending order.

Accordingly, the priorities of the cell selection candidates are updatedon each occasion. Thus, it is possible to flexibly respond to change inthe radio propagation environment and reduce the power consumption ofthe LC-MTC UE.

Third Embodiment

The paging repetitions are being studied for LC-MTC requiring coverageenhancement. The repeated transmission improves the reception quality inthe LC-MTC UEs in the enhanced coverage areas.

Since the paging repetitions are not conventionally performed, 3GPP isstudying new methods for the paging repetitions. Non-Patent Document 11discloses a method for repeated paging transmission across subframes asa method for the paging repetitions.

However, none of the details of the structure of the subframes forpaging transmission is disclosed. Thus, it becomes unclear whichsubframe the LC-MTC UE should receive, and the LC-MTC UE cannot receivepagings including repetitions.

The third embodiment will disclose a detailed method for the pagingrepetitions. The paging transmission including the repetitions areperformed across radio frames. The transmission may be performed throughconsecutive radio frames. An initial paging may be transmitted on radioframes and subframes that are derived by the conventional method forderiving paging frames (PFs) and paging occasions (POs) (see Non-PatentDocument 2).

The PFs and the POs are derived using a discontinuous receptionparameter such as a discontinuous reception (DRX) period notified byupper-layer signaling, and a UE identifier (UE-ID). The POs are limitedto the subframes whose subframe numbers are 0, 4, 5, and 9 for frequencydivision duplex (FDD), whereas the POs are limited to the subframeswhose subframe numbers are 0, 1, 5, and 9 for time division duplex(TDD).

The pagings are consecutively transmitted across radio frames forrepeated transmission from the initial radio frame. The subframes forrepeated paging transmission have the same subframe numbers as thosederived at the initial transmission. The LC-MTC UE may receive thepagings for initial transmission and repeated transmission across theradio frames and the subframes that are derived in such a manner.

Accordingly, the LC-MTC UE can receive the pagings including therepetitions. Thus, the LC-MTC UEs in the enhanced coverage areas canreceive the pagings.

The LC-MTC UE may finish receiving the repeated transmission oncesecuring a desired reception quality, without receiving all the initialtransmission and the repeated transmission. Accordingly, since thereception operations of the LC-MTC UE can be reduced, the powerconsumption can be reduced. Furthermore, since the paging reception canbe finished earlier and operations after the paging reception can bestarted earlier, a delay time can be shortened.

FIG. 12 is a conceptual diagram illustrating an example method forrepeated paging transmission according to the third embodiment. In FIG.12, a reference numeral “121” denotes a paging frame (PF) that is aradio frame RF for initial paging transmission. Furthermore, a referencenumeral “122” denotes a structure of subframes SF in the radio frame RF.

The radio frame RF consists of the ten subframes SF whose subframenumbers range from 0 to 9. The diagonally hatched subframe SF is apaging occasion (PO) that is the subframe SF for initial pagingtransmission. The PO that is the subframe SF for initial pagingtransmission has the subframe number “9”.

in FIG. 12, a reference numeral “123” denotes the radio frame RF forrepeated paging transmission. The pagings for repeated transmission asmany as the number of repetitions are consecutively transmitted from thePF that is the radio frame RF for initial paging transmission. Thenumber of repetitions is “2” herein. The structure of the subframes SFwithin the radio frames RF that are for repeated paging transmission isthe same as that of the subframes SF in the PF that is the radio frameRF for initial paging transmission.

Thus, the subframes for repeated paging transmission have the subframenumber “9”. The PFs/POs for initial paging transmission, and the radioframes RF and the subframes SF for repeated paging transmission arerepeatedly transmitted on a discontinuous reception period T.

The number of paging repetitions may be determined for each cell or foreach of the LC-MTC UEs. The number of repetitions may be determined by acell. The cell may determine the number of repetitions using, forexample, a reception quality, a CQI, or CSI in the LC-MTC UE.Furthermore, the cell may obtain the capability of the LC-MTC UE anddetermine the number of repetitions using the capability. The followingtwo examples (1) and (2) will be disclosed as specific examples of amethod for recognizing the number of paging repetitions by the LC-MTCUE.

(1) The number of paging repetitions is notified by the SI for theLC-MTC UE. The method is effective when the number of paging repetitionsis notified for each cell or each of the LC-TC UEs. Accordingly, thenumber of paging repetitions can be received irrespective of an RRCstate (RRC_Idle, RRC_Connected) of the LC-MTC UE.

(2) The number of paging repetitions is notified by RRC signaling. Here,the number of paging repetitions may be notified in the initial access.The method may be applied when the number of paging repetitions isnotified for each cell or each of the LC-MTC UEs. A larger amount ofparameters can be notified than that when the number of pagingrepetitions is notified by the MIB or the SI. Furthermore, the amount ofinformation to be notified by the MIB or the SI can be reduced.

Accordingly, the LC-MTC UE can receive the pagings for initialtransmission and repeated transmission.

Although the method for repeated paging transmission on the radio framesthat are consecutive from the initial transmission is described above,another method will be disclosed. The repeated paging transmission maybe performed at predetermined radio frame intervals from the initialtransmission.

For example, when the number of paging repetitions is 2, thepredetermined radio frame intervals are 3, and the radio frame number ofthe radio frame for initial paging transmission is 25, the firstrepetition is transmitted by the radio frame whose radio frame number is28, and the second repetition is transmitted by the radio frame whoseradio frame number is 31. When the predetermined radio frame intervalsare 1, the radio frames may be consecutive.

Accordingly, even in the paging repetitions, the resources can beflexibly scheduled.

The predetermined radio frame intervals may be statically predetermined,for example, in a standard. Furthermore, the intervals may bepredetermined for each cell or for each of the LC-MTC UEs. The methodfor recognizing the number of paging repetitions may be applied to amethod for recognizing the predetermined radio frame intervals by theLC-MTC UE. Accordingly, the LC-MTC UE can recognize the predeterminedradio frame intervals and receive the pagings for initial transmissionand repeated transmission.

A period derived from the number of repetitions and the radio frameintervals at which the paging is transmitted may be set smaller than thediscontinuous reception period T. Accordingly, only the same paging istransmitted within the same discontinuous reception period, and theLC-MTC UE never receives more pagings within the same discontinuousreception period. Accordingly, the paging process in the LC-MTC UE canbe simplified.

Since the LC-MTC UE can receive the pagings repeatedly transmitted,using the method disclosed in the third embodiment, it can receive thepagings while satisfying the demand for coverage enhancement.Accordingly, a stable communication system can be built.

Furthermore, the subframes for repeated transmission can be replacedwith subframes for the conventional paging transmission by repeating thepaging transmission across the consecutive radio frames or atpredetermined radio frame intervals. Accordingly, the pagingtransmission can be repeated without influencing the configuration ofMBSFN subframes.

Although FIG. 12 illustrates that the subframes for repeated pagingtransmission are identical to the subframes for initial pagingtransmission, a case where the subframes for repeated pagingtransmission are different from the subframes for initial pagingtransmission will be disclosed. The subframes for repeated pagingtransmission may be derived from the number of repetitions. Taking FDDas an example, when the number of repetitions is 2, the first repeatedtransmission is performed by the subframe whose subframe number is 0,and the second repeated transmission is performed by the subframe whosesubframe number is 4.

In an alternative example, a subframe for the n-th repeated transmission(n is a natural number) may have a subframe number associated with avalue obtained from “n mod 4”.

Taking FDD as an example, the subframe may be: a subframe whose subframenumber is 0 when the value obtained from “n mod 4” is 0; a subframewhose subframe number is 4 when the value obtained from “n mod 4” is 1;a subframe whose subframe number is 5 when the value obtained from “nmod 4” is 2; or a subframe whose subframe number is 9 when the valueobtained from “n mod 4” is 3.

Here, “n mod 4” indicates a remainder left when “n” is divided by 4 thatis the number of subframes for repeated pagings. The number of subframesfor repeated pagings may be not limited to 4 but is defined as 1 atminimum and 10 at maximum.

As such, setting the subframe for repeated paging transmission to thesubframe whose subframe number is associated with the value obtainedfrom “n mod 4” enables the subframe for repeated paging transmission tobe dispersed into subframes and be more flexibly scheduled. Thesederiving methods may be statically predetermined, for example, in astandard.

The subframe number associated with the value obtained from “n mod 4”may be a subframe number with which the conventional paging transmissionis possible. Accordingly, since the subframes for repeated pagingtransmission can be replaced with the subframes for the conventionalpaging transmission, the paging transmission can be repeated withoutinfluencing the configuration of the MBSFN subframes.

First Modification of Third Embodiment

With the method disclosed in the third embodiment, the pagingtransmission is repeated across radio frames according to the number ofpaging repetitions. Consequently, an amount of delay until the LC-MTC UEreceives the pagings increases. Accordingly, a delay in receiving, forexample, the incoming call information, SI modification, an earthquakeand tsunami warning system (ETWS) indication, a commercial mobile alertsystem (CMAS) indication that are included in the pagings, and a controldelay occur.

The first modification will disclose a method for reducing this controldelay. The paging transmission is repeated across the consecutivesubframes from a subframe for initial paging transmission. The initialpaging may be transmitted across the radio frames and the subframes thatare derived by the conventional method for deriving the PFs and the POs,similarly as the method disclosed in the third embodiment.

Accordingly, the LC-MTC UE can receive the pagings including therepetitions with a smaller amount of delay.

FIG. 13 is a conceptual diagram illustrating an example method forrepeated paging transmission according to the first modification of thethird embodiment. In FIG. 13, a reference numeral “131” denotes a PFthat is a radio frame RF for initial paging transmission. Furthermore, areference numeral “132” denotes a structure of subframes SF in the PFthat is the radio frame RF for initial paging transmission. The firstdiagonally-hatched subframe SF is a PO that is the subframe SF forinitial paging transmission. The PO that is the subframe SF for initialpaging transmission has the subframe number “9”.

In FIG. 13, a reference numeral “133” denotes the radio frames RF forrepeated paging transmission. Furthermore, a reference numeral “134”denotes a subframe SF for repeated paging transmission. The pagings forrepeated transmission as many as the number of repetitions (i.e.,repetition number abbreviated as RPN) are consecutively transmitted fromthe PO that is the subframe SF for initial paging transmission. Therepetition number (RPN) is “2” herein.

The subframes SF for repeated paging transmission may extend over radioframes RF. Among subframes SF of a radio frame RF that is next to theradio frame RF131 for initial paging transmission, the repeated pagingtransmission is performed on subframes SF whose subframe numbers are 0and 1. The PFs/POs for initial paging transmission, and the radio framesRF and the subframes SF for repeated paging transmission are repeatedlytransmitted at the discontinuous reception period T.

Although the repeated paging transmission is performed on theconsecutive subframes from the initial transmission in the methoddescribed above, the repeated paging transmission may be performed atpredetermined subframe intervals from the initial transmission as analternative method.

For example, when the number of paging repetitions is 2, thepredetermined subframe intervals are 3, and for initial pagingtransmission, the radio frame number of the radio frame is 25 and thesubframe number of the subframe is 9, the first repetition istransmitted by the subframe whose subframe number is 2 in the radioframe whose radio frame number is 26. The second repetition istransmitted by the subframe whose subframe number is 5 in the radioframe whose radio frame number is 26. When the predetermined subframeintervals are 1, the subframes may be consecutive.

Accordingly, even in the paging repetitions, the resources can beflexibly scheduled.

The predetermined radio frame intervals may be statically predetermined,for example, in a standard. Furthermore, the intervals may bepredetermined for each cell or for each of the LC-MTC UEs. The methodfor recognizing the number of paging repetitions that is disclosed inthe third embodiment may be applied to a method for recognizing thepredetermined radio frame intervals by the LC-MTC UE. Accordingly, theLC-MTC UE can recognize the predetermined radio frame intervals andreceive the pagings for initial transmission and repeated transmission.

Furthermore, the subframes for repeated paging transmission may belimited to the subframes for the conventional paging transmission as analternative method. Examples of the subframes for FDD include subframeswhose subframe numbers are 0, 4, 5, and 9.

For example, when the number of paging repetitions is 2, thepredetermined subframe intervals are 1, and for initial pagingtransmission, the radio frame number of the radio frame is 25 and thesubframe number of the subframe is 9, the first repetition istransmitted by the subframe whose subframe number is 0 in the radioframe whose radio frame number is 26. The second repetition istransmitted by the subframe whose subframe number is 4 in the radioframe whose radio frame number is 26.

Accordingly, since the subframes for paging repetitions can be replacedwith the subframes for the conventional paging transmission, the pagingtransmission can be repeated without influencing the configuration ofthe MBSFN subframes.

Since the LC-MTC UE can receive the pagings repeatedly transmitted,using the method disclosed in the first modification, it can receive thepagings while satisfying the demand for coverage enhancement.Accordingly, a stable communication system can be built.

Furthermore, the LC-MTC UE can receive the pagings including therepetitions with a smaller amount of delay than that by the methoddisclosed in the third embodiment. Accordingly, a control delay fornotifying the pagings can be reduced. Particularly, the method herein iseffective at notifying the urgent ETWS indication.

Second Modification of Third Embodiment

When the MBSFN subframes are configured in a cell, a new problem arises.Since the MBSFN subframes cannot receive and transmit the pagings, thePOs on which the pagings have been conventionally transmitted arerestricted to subframes in which MBSFN subframes cannot be configured.

Under a circumstance in which subframes capable of configuring the POsare restricted, the subframes for repeated transmission sometimescollide with the MBSFN subframes when the paging repetitions asdisclosed in the first modification of the third embodiment areperformed. When the subframes for repeated transmission collide with theMBSFN subframes, pagings cannot be transmitted on the MBSFN subframes.Thus, the LC-MTC UEs have a problem with incapability of receiving thepagings.

The second modification will disclose a method for solving this problem.Transmission of the pagings on the MBSFN subframes is enabled. Thedownlink control information (DCI) for paging is transmitted on theMBSFN subframes to enable the paging transmission. Hereinafter, thedownlink control information for paging may be referred to as the pagingdownlink control information.

The paging downlink control information is mapped to an enhancedphysical downlink control channel (EPDCCH) or a PDCCH. The EPDCCH or thePDCCH to which the paging downlink control information has been mappedis transmitted on the MBSFN subframes. The PDSCH to which the paging ismapped is transmitted on a subframe identical to that on which thepaging downlink control information is transmitted.

The paging downlink control information may contain subframe informationto which the paging-mapped PDSCH is mapped as an alternative method.Accordingly, the paging-mapped PDSCH and the paging downlink controlinformation can be transmitted on different subframes.

The paging downlink control information is masked by a pagingindication-radio network temporary identifier (PI-RNTI). Throughdetection of the PI-RNTI, the LC-MTC UE can recognize the existence ofthe paging and receive the paging downlink control information. TheLC-MTC UE can receive scheduling information on the paging-mapped PDSCHupon receipt of the paging downlink control information. The LC-MTC UEreceives the PDSCH according to the scheduling information on thepaging-mapped PDSCH, and then receives the paging.

The pagings not only for repeated transmission but also for initialtransmission may be transmitted on the MBSFN subframes. Here, theconfiguration of the subframes (POs) on which the pagings aretransmitted may be provided in addition to the conventional subframenumbers. Accordingly, since the subframes capable of configuring the POsincrease, it is possible to support a case where Ns that is the numberof MTC UEs is increased to match the tremendous number of MTCs.

Not the paging downlink control information but the paging-mapped PDSCHmay be transmitted on the MBSFN subframes as an alternative method.Assuming that only the repeated transmission is performed on the MBSFNsubframes, the downlink control information for paging repetitions maybe identical to that for initial transmission. The schedulinginformation on the PDSCH to which the initial transmission is mapped maybe identical to that of the PDSCH to which the repeated transmission ismapped. The LC-MTC UE can receive the PDSCH to which the repeatedtransmission is mapped by obtaining the scheduling information on thePDSCH to which the initial transmission is mapped.

Alternatively, the downlink control information for initial pagingtransmission may contain the downlink control information for pagingrepetitions. The downlink control information for initial pagingtransmission contains not only the scheduling information on the PDSCHto which the initial transmission is mapped but also the schedulinginformation on the PDSCH to which the repeated transmission is mapped.Upon receipt of the downlink control information for initial pagingtransmission, the LC-MTC UE can obtain the scheduling information on thePDSCH to which the repeated transmission is mapped, and receive thePDSCH.

Alternatively, the downlink control information for initial pagingtransmission may contain subframe information for repeated pagingtransmission. Examples of the subframe information include informationindicating subframe numbers and information indicating radio framenumbers. The scheduling information on the PDSCH to which the initialpaging transmission is mapped may be identical to that of the PDSCH towhich the repeated paging transmission is mapped.

Upon obtainment of the scheduling information on the PDSCH to which theinitial transmission is mapped, the LC-MTC UE can recognize thesubframes for repeated transmission, and receive, on the subframes, thePDSCH to which the repeated transmission is mapped.

The MBSFN subframes for paging transmission may be limited to thesubframes on which the PMCH is not transmitted. Accordingly, even whenthe MBSFN subframes include subframes to which the PMCH that is aphysical channel for MBMS is mapped, the pagings can be transmittedthereon. Here, the method for designating, by an eNB, a subframe forrepeated transmission may be used, for example. A subframe to which thePMCH is not mapped from among the MBSFN subframes may be designated asthe subframe for repeated transmission.

According to the method disclosed in the second modification, thepagings can be transmitted on the MBSFN subframes. Thus, it is possibleto solve a problem with the collision of the subframes for repeatedpaging transmission with the MBSFN subframes and a problem of the LC-MTCUE with incapability of receiving the pagings. Accordingly, since theLC-MTC UE can receive the pagings repeatedly transmitted, it can receivethe pagings while satisfying the demand for coverage enhancement.Accordingly, a stable communication system can be built.

Furthermore, the LC-MTC UE can receive the pagings including therepetitions with a smaller amount of delay than that by the methoddisclosed in the third embodiment. Accordingly, a control delay fornotifying the pagings can be reduced. Particularly, the method iseffective at notifying the urgent ETWS indication.

The method disclosed in the second modification may be applied tosubframes for transmitting the system information (SI) to be disclosedin the fifth embodiment later. The pagings may be replaced with thesystem information. The DCI for SI may be masked by a systeminformation-radio network temporary identifier (SI-RNTI). Accordingly,the SI can be transmitted on the MBSFN subframes. The LC-MTC UE canreceive the SI. The same advantages as described above can be produced.

Furthermore, the method disclosed in the second modification may beapplied to subframes for transmitting a random access response (RAR).The pagings may be replaced with the RAR. The DCI for RAR may be maskedby a random access-radio network temporary identifier (RA-RNTI).Accordingly, the RAR can be transmitted on the MBSFN subframes. TheLC-MTC UE can receive the RAR. The same advantages as described abovecan be produced.

It is expected that the number of the LC-MTC UEs will be tremendous.Thus, the number of subframe; on which the pagings are transmitted maybe increased. Although the conventional number of such subframes is fouras described above, it may be increased to 5 or more. Furthermore, thesubframes on which the POs are generated may be provided across radioframes. The method to be disclosed later may be applied thereto.

Another method for solving the problems disclosed in the secondmodification will be hereinafter disclosed. The subframes for repeatedpaging transmission are determined from among the subframes excludingthe MBSFN subframes.

FIG. 14 is an example sequence diagram when the subframes for repeatedpaging transmission according to the second modification of the thirdembodiment are determined from among the subframes excluding the MBSFNsubframes.

In Step ST1401, an MCE notifies an eNB of MBSFN subframe configurationinformation.

In Step ST1402, the eNB determines an MBSFN subframe configuration.Here, the eNB may determine the MBSFN subframe configuration also inconsideration of the MBSFN subframes necessary to be used except forMBMS for each cell. Accordingly, the MBSFN subframe configuration forthe cell is determined.

In Step ST1403, the LC-MTC UE notifies the eNB of UE capabilityinformation. The UE capability information is notified through dedicatedRRC signaling. The eNB that has received the UE capability informationrecognizes that the UE is an LC-MTC UE.

In Step ST1404, the eNB determines whether repetitions are necessary onthe basis of a downlink reception quality report from the LC-MTC UE andan uplink reception quality in the LC-MTC UE. Whether the repetitionsare necessary may be determined by setting a predetermined threshold andusing the threshold. When it is determined that the repetitions arenecessary, the processes proceed to Step ST1405. When it is determinedthat the repetitions are unnecessary, the processes proceed to StepST1407.

In Step ST1405, the eNB determines the number of repetitions. Here, thenumber of repetitions also may be determined by setting a thresholdaccording to the number of repetitions and using the threshold. Acombined process of Step ST1404 and Step ST1405 may be performed.

In Step ST1406, the eNB determines a repetition subframe configuration.The subframes corresponding to the number of repetitions may be selectedfrom among subframes excluding the subframes configured as the MBSFNsubframes.

In Step ST1407, the eNB notifies the LC-MTC UE of the number ofrepetitions and the repetition subframe configuration information.

The LC-MTC UE that has received the number of repetitions and therepetition subframe configuration information performs the discontinuousreception in Step ST1408. The LC-MTC UE receives the pagings as many asthe number of repetitions. The LC-MTC UE determines that the initialpaging transmission is performed on a PF/PO and that the repetitions areperformed on the repetition subframes as many as the number ofrepetitions notified in Step ST1407.

On which one of the repetition subframes the paging repetition isperformed may be predetermined, for example, in a standard. It may bedetermined, for example, that the repeated transmission is performed inascending order of the subframe numbers in the repetition subframes fromthe subframe (PO) for initial paging transmission. Alternatively, theeNB may associate repetition numbers with the repetition subframeshaving the repetition numbers, and notify the UE of the association inStep ST1407. When the number of the repetition subframes is small andless than the number of repetitions, repetition subframes in the nextradio frame may be used.

Accordingly, the UE can receive the paging repetitions. Furthermore, acollision between the repeated paging transmission and the MBSFNsubframes can be avoided. Furthermore, the subframes that are notactually used as the MBSFN subframes can be used for repeatedtransmission. Thus, the earlier paging transmission can be performed,the UE can receive the pagings earlier, and a delay in the pagingprocess can be reduced.

After determination on the repetition subframe configuration, when theconfiguration of the MBSFN subframes is changed, the repetition subframeconfiguration may be re-determined. The re-determined repetitionsubframe configuration may be notified to the LC-MTC UE. Accordingly,flexible operations of MBMS and the other uses using MBSFN subframesbecome possible.

Furthermore, when the eNB configures the MBSFN subframes for each cellfor other uses except for the MBMS, the MBSFN subframes may beconfigured for each cell for such use in consideration of the number ofrepetitions necessary for the LC-MTC UE. The subframes as many as thenumber of repetitions necessary for the LC-MTC UE may be reserved, andthe other subframes may be determined as the MBSFN subframes. Since therepeated transmission to the LC-MTC UE can be prioritized, a delay inthe paging process can be further reduced.

Third Modification of Third Embodiment

Conventionally, the paging has been received in the following manner. APDCCH of a subframe (PO) in a radio frame (PF) derived using anidentifier of a UE is received, and a PI-RNTI masked by the pagingdownlink control information is detected to receive the paging downlinkcontrol information. The LC-MTC UE receives a PDSCH to which the pagingis mapped, according to the received paging downlink controlinformation.

It is necessary to perform on the LC-MTC UEs supporting the coverageenhancement not only the repeated paging transmission but also therepeated transmission of the PDCCH to which the paging downlink controlinformation is mapped. The repeated transmission improves the receptionquality of the PDCCH of the LC-MTC UE in an extended coverage area andenable the LC-MTC UE to receive the paging downlink control information.

The methods disclosed from the third embodiment to the secondmodification thereof may be applied to a method for repeatedlytransmitting the PDCCH to which the paging downlink control informationis mapped and to a method for receiving the PDCCH by the LC-MTC UE.

The following two examples (1) and (2) will be disclosed as examplerelationships between the method for repeatedly transmitting the PDCCHto which the paging downlink control information is mapped and therepeated paging transmission method.

(1) After the initial transmission and the repeated transmission of thePDCCH, the pagings for initial transmission and repeated transmissionare transmitted. The initial paging transmission is performed on thesubframes identical to those on which the last repetition oftransmission of the PDCCH is performed or on subframes after k subframes(k is an integer larger than or equal to 1).

(2) The initial transmission of the PDCCH and the initial pagingtransmission are performed on the same subframe, and the repeatedtransmissions of the PDCCH and repeated paging transmissions areperformed on the respective same subframes.

In the method (1) above, the LC-MTC UE can start receiving the pagingsafter being able to receive the PDCCH to which the paging downlinkcontrol information is mapped including the repetitions. Thus, theLC-MTC UE can obtain the paging downlink control information, forexample, scheduling information on a resource to which the paging ismapped, etc. by receiving the PDCCH including the repetitions. TheLC-MTC UE can receive the PDSCH to which the paging is mapped, using theobtained information.

When compared with the method (2) above, the method (1) above does notrequire storage of information on the subframes on which the initial andrepeated transmissions of the PDCCH are performed. Since there is noneed to prepare a memory, a buffer, etc. for storing the information,the configuration of the LC-MTC UE can be simplified.

According to the method (2) above, the PDCCH to which the pagingdownlink control information is mapped and the paging are transmitted onthe same subframe. Here, the LC-MTC UE may store the receivinginformation on subframes for the total number of the subframes forinitial transmission and the maximum number of repetitions. When theLC-MTC UE can receive the PDCCH to which the paging downlink controlinformation is mapped, the paging transmitted on the same subframe canbe received using the paging downlink control information. The LC-MTC UEmay have a memory, a buffer, etc. for storage. Since the LC-MTC UE canreceive the pagings earlier than by the method (1) above, a controldelay time can be shortened.

The LC-MTC UEs that support the reduced bandwidth cannot receive theconventional PDCCH transmitted across the system bandwidth. Thus, theLC-MTC UEs cannot receive the pagings in the conventional pagingtransmitting and receiving methods.

The third modification will disclose a method for solving this problem.A paging of the LC-MTC UE is mapped to the PDSCH. The paging downlinkcontrol information of the LC-MTC UE, for example, the schedulinginformation on the PDSCH to which the paging is mapped, etc. is mappedto an EPDCCH. The EPDCCH is mapped to a predetermined number of resourceblocks (RBs) in a PDSCH region within one subframe. Since the resourcesto which the paging downlink control information is mapped can be set tonarrow bandwidths, the LC-MTC UEs that support the reduced bandwidth canreceive the paging.

An RNTI for masking the paging downlink control information on theEPDCCH may be a PI-RNTI. Alternatively, the RNTI may be newly providedfor the LC-MTC UEs. The RNTI may be, for example, an MTC-PI-RNTI.Distinction from the conventional UEs is enabled by newly providing theRNTI for the LC-MTC UEs. With use of the MTC-PI-RNTI in detectingcontrol information, the control information can be identified as thatfor the LC-MTC UEs, and a malfunction can be reduced.

The paging downlink control information for the conventional UEs (legacyUEs) may be transmitted using the PDCCH, and the paging downlink controlinformation for the LC-MTC UEs may be transmitted using the EPDCCH.Here, the paging downlink control information to be mapped to the EPDCCHmay be masked by the MTC-PI-RNTI. The LC-MTC UE receives the EPDCCH onsubframes of the PFs/POs derived for paging. Upon detection of thepaging downlink control information masked by the MTC-PI-RNTI, theLC-MTC UE receives the PDSCH according to the paging downlink controlinformation to receive the paging.

When the EPDCCH is used for transmitting the paging downlink controlinformation as described above, an additional problem occurs. Since theEPDCCH is transmitted on predetermined resource blocks (RBs), the LC-MTCUE does not know on which resource the EPDCCH is transmitted on thesubframes of the PFs/POs derived for paging. Thus, the LC-MTC UE cannotreceive the EPDCCH.

Non-Patent Document 12 discloses a method for solving this problem.Specifically, Non-Patent Document 12 discloses a method for schedulingan EPDCCH for paging. The method is a method for mapping, into sixresource blocks at the center of the carrier, an EPDCCH for commonmessage that includes SIBs, pagings, and RAR, or a method for including,in an MIB, information indicating whether the resource blocks of theEPDCCH are allocated at predetermined positions or frequency hopping isperformed.

However, when the resources to which the EPDCCH for paging is mapped arefixed to the six resource blocks at the center of the carrier, a problemwith degradation in reception quality occurs due to the susceptibilityto the frequency fading. Furthermore, when the frequency hopping isperformed, how to notify a frequency hopping pattern comes intoquestion. When the information is included in the MIB and notified, anamount of information in the MIB increases. Furthermore, since the MIBis repeatedly notified, the amount of resources required for thenotification will become excessive. Thus, a problem with decrease inefficiency of resource usage occurs.

The third modification will disclose a method for solving this problem.The resources on which the EPDCCH is transmitted are predetermined, forexample, in a standard. Here, the paging downlink control information ismapped to the EPDCCH.

The following seven examples (1) to (7) are disclosed as examples ofinformation on the resources on which the EPDCCH is transmitted.

(1) The number of resource blocks (RBs)

(2) Allocation of the RBs; the first RB number may be used.

(3) A configuration of a reference signal (RS); a sequence of the RSs orthe sequence number thereof may be used.

(4) The number of repetitions

(5) The frequency hopping mode

(6) A frequency hopping pattern

(7) A combination of (1) to (6) above

The information on the resources on which the EPDCCH is transmitted maybe any as long as the LC-MTC UE can identify a resource to which theEPDCCH is mapped. The information may be scheduling information on theEPDCCH. As such, predetermining the information, for example, in astandard can prevent increase in the amount of information in the MIBand decrease in the efficiency of resource usage.

The information on the resources of the EPDCCH to which the pagingdownlink control information is mapped may have multiple options.Information groups on the resources on which the EPDCCH is transmittedmay have multiple options. The information on the resources of theEPDCCH to which the paging downlink control information is mapped or theinformation groups on the resources on which the EPDCCH is transmittedare made to have multiple options, so that cells can change theresources on which the EPDCCH is transmitted, depending on a radiopropagation state. Here, the paging downlink control information ismapped to the EPDCCH.

Accordingly, a communication system resilient to change in the radiopropagation state can be built. Furthermore, when the repetition ofreception of the EPDCCH to which a paging control signal is mapped isperformed, the number of the repetitions can be reduced. Thus, the powerconsumption of the LC-MTC UE can be reduced.

However, mere provision of the groups does not allow the LC-MTC UE torecognize which one of the groups is to be used. Here, the resources onwhich the EPDCCH for all of the groups is transmitted may be receivedand detected with the MTC-PI-RNTI, according to the information on allof the groups. However, reception of the EPDCCHs for all of the groupscomplicates the operations of the LC-MTC UE and increases the powerconsumption.

In order to solve such a problem, an indicator associated with theinformation on the resource of each of the EPDCCHs may be provided. Anindicator associated with each of the information groups on theresources on which the EPDCCH is transmitted may be provided. Theindicators and information on the resources of the EPDCCH for each ofthe groups are predetermined in a table, for example, in a standard. TheLC-MTC UEs stores the table.

A cell may use the indicators to notify the LC-MTC UE of whichinformation on the resource of the EPDCCH is valid. The cell notifiesthe LC-MTC UE of the indicators.

The following three examples (1) to (3) are disclosed as specificexamples of methods for notifying the indicators.

(1) The indicators are included in the MIB and broadcasted.

(2) The indicators are included in the SIB including SI for the LC-MTCUE and notified.

The LC-MTC UE can recognize to which resource the EPDCCH to which thevalid paging downlink control information is mapped is allocated, byreceiving the MIB or the SIB for the LC-MTC UE to obtain the indicators.The information included in the MIB or the SIB for the LC-MTC UE may beonly the indicators, thus enabling notification with a smaller amount ofinformation. Accordingly, a communication system that can preventdecrease in the efficiency of resource usage to a minimum and that isresilient to change in the radio propagation state can be built.

(3) The indicators are notified by RRC signaling; here, the indicatorsmay be notified in the initial access. The method may be applied whenthe indicators are provided for each cell or each of the LC-MTC UEs. Alarger amount of parameters can be notified than that when theindicators are notified by the MIB or the SI. Furthermore, the amount ofinformation to be notified by the MIB or the SI can be reduced. Usingthe same indicators within the same TAC may be predetermined, forexample, in a standard.

The third modification will disclose another method for solving theproblems. A method for deriving information on the resources on whichthe EPDCCH is transmitted is predetermined. Here, the paging downlinkcontrol information is mapped to the EPDCCH. The deriving method may bepredetermined, for example, in a standard. A derivation function may beprovided. The derivation function may be a function using at least oneof a PF, a PO, and an UE identifier (UE-ID) as an input parameter. Theoutput parameter may be information on the resources on which the EPDCCHis transmitted. Alternatively, the output parameter may be theindicators. The indicators and information on the resources on which theEPDCCH is transmitted may be predetermined in a table, for example, in astandard. The LC-MTC UE stores the table.

Accordingly, since there is no need to include the indicators in the MIDor the SIB for the LC-MTC UE, it is possible to prevent decrease in theefficiency of resource usage. Furthermore, through determination of atleast one of a PF and a PO as the input parameter of the derivationfunction, a different resource is allocated when at least one of the PFand the PO is different. Accordingly, concentration on a particularresource can be prevented. Furthermore, since a different resource isallocated to each UE using the UE-ID as the input parameter of thederivation function, the concentration on a particular resource can beprevented.

If the concentration on a particular resource occurs, it is possible toprevent any one of the paging downlink control information items frombeing mapped to the EPDCCH. The paging downlink control information itemmay be mapped to the EPDCCH for the next PF/PO. However, a problem witha delay in notifying the paging occurs. Such a problem can be solved bypreventing the concentration on a particular resource as the methodabove.

With the method according to the third modification, the LC-MTC UE canreceive the EPDCCH to which the paging downlink control information ismapped and detect the presence or absence of the paging. If the pagingexists, the paging can be received.

Although mapping the paging downlink control information for the LC-MTCUE to the EPDCCH is disclosed, the paging downlink control informationfor the LC-MTC UE may be mapped not only to the EPDCCH but to a physicaldownlink control channel using a narrow-bandwidth resource. The physicaldownlink control channel may be any physical downlink control channelconfigured within a bandwidth at which the LC-MTC UEs that support thereduced bandwidth are capable of reception.

The relationship between the method for repeatedly transmitting thePDCCH to which the paging downlink control information is mapped and therepeated paging transmission method as described above may be applied toa relationship between the method for repeatedly transmitting the EPDCCHto which the paging downlink control information is mapped and therepeated paging transmission method. The LC-MTC UEs that support thecoverage enhancement can receive the paging downlink controlinformation, and the pagings using the paging downlink controlinformation.

Fourth Embodiment

The subframes for initial paging transmission are sometimes identical tothe subframes for repeated paging transmission.

FIG. 15 is a conceptual diagram when the subframes for initial pagingtransmission are identical to the subframes for repeated pagingtransmission. An example case where the repeated transmission isperformed on the same subframes in consecutive radio frames as disclosedin the first modification of the third embodiment will be described.

Assume that a SFN of a radio frame is 25 (SFN=25), the subframe numberof the subframe is 9 for initial paging transmission by an LC-MTC UE A,and the number of repetitions is 2. For example, an initial transmission(IN(A)) is performed on a radio frame (RF) 151 whose SFN is 25. Therepeated transmission is performed on subframes whose subframe number isthe same as that of the initial transmission, specifically, thesubframes (SF9) whose subframe number is 9, in two radio frames 152 and153 that are consecutive from the radio frame 151 for initialtransmission (RP#1(A) and RP#2(A)).

The PFs/POs for paging transmission are determined by an identifier ofan LC-MTC UE. Thus, different UEs may have different PFs/POs. Assumethat a SFN of a radio frame is 26 (SFN=26), the subframe number of thesubframe is 9 for initial paging transmission by an LC-MTC UE B, and thenumber of repetitions is 2.

For example, an initial transmission (IN(B)) is performed on the radioframe (RF) 152 whose SFN is 26. The repeated transmission is performedon subframes whose subframe number is the same as that of the initialtransmission, specifically, the subframes (SF9) whose subframe number is9, in two radio frames 153 and 154 that are consecutive from the radioframe 152 for initial transmission (RP#1(B) and RP#2(B)).

Here, the initial transmission of the LC-MTC UE B and the repeatedtransmission of the LC-MTC UE A are performed on the radio frame 152whose SFN is 26 and on the subframe whose subframe number is 9. It isunclear how to multiplex the paging for repeated transmission of theLC-MTC UE A and the paging for initial transmission of the LC-MTC UE B.

The fourth embodiment will disclose a method for solving such a problem.A paging message may be created by multiplexing the paging for initialtransmission and the paging for repeated transmission in the same pagingmessage, and mapped to the PDSCH. The mapping may be performed perrepetition number.

The LC-MTC UE detects the EPDCCH to which the paging DCI is mapped,using the PI-RNTI or the MTC-PI-RNTI to receive the paging DCI. TheLC-MTC UE receives the PDSCH according to the received paging DCI toobtain the paging message created by multiplexing the paging for initialtransmission and the paging for repeated transmission.

The LC-MTC UE to which the paging for initial transmission istransmitted on the subframe receives the paging for initial transmissionin the paging message. The LC-MTC UE to which the pagings for repeatedtransmission are transmitted on the subframes receives the pagings forrepeated transmission corresponding to the repetition number in thepaging message.

FIG. 16 illustrates an example paging message according to theconventional technique. The paging message includes paging record listinformation for incoming call (pagingRecordList), SI modificationinformation (systemInfoModification), ETWS information(etws-Indication), CMAS information (cmas-Indication), and EAB parametermodification information (eab-ParamModification).

The paging record list information for incoming call (pagingRecordList)includes one or more paging record information items (pagingRecord). Thepaging record information items include a UE identifier indicating an UEto be called by an incoming call. The paging record information itemsmay include core network domain (CN domain) information. Examples of theUE identifier include a serving-temporary mobile subscriber identity(s-TMSI) and an international mobile subscriber identity (IMSI).

FIG. 17 illustrates an example paging message according to the fourthembodiment. The paging message includes pagings for initial transmissionand for repeated transmission. A portion enclosed by a dashed rectanglein FIG. 17 is a paging for repeated transmission. The paging is a pagingwhose repetition number is 1. The paging for repeated transmission maybe limited to the paging record list information for incoming call(pagingRecordList_repetition#1).

The paging record list information for incoming call that is intendedfor repeated transmission includes one or more paging record informationitems for repeated transmission. The paging record information itemsinclude a UE identifier indicating an UE to be called by an incomingcall. The paging record information items may include the CN domaininformation. Examples of the UE identifier include a s-TMS1 and an IMSI.

The paging for repeated transmission may exclude information to betransmitted not separately for each of the LC-MTC UEs. Examples of suchinformation include the SI modification information, the ETWSinformation, and the CMAS information. The EAB parameter modificationinformation may be applied not to each of the UEs but all the LC-MTCUEs. If the EAB parameter modification information is applied to all theLC-MTC UEs, the paging for repeated transmission may exclude theinformation. The paging for repeated transmission may include the EABparameter modification information for each of the UEs.

Accordingly, even when the subframes for initial paging transmission areidentical to the subframes for repeated paging transmission, the cellcan transmit both the initial transmission and the repeatedtransmission. Thus, the LC-MTC UE can receive the initial transmissionor the repeated transmission as appropriate.

Furthermore, the DC for initial paging transmission can be identical tothe DCI for repeated paging transmission. Thus, the resource of theEPDCCH to which the DCI for initial transmission is mapped may beidentical to that of the EPDCCH to which the DCI for repealedtransmission is mapped.

Since the LC-MTC UE can receive the paging upon receipt of the pagingPDSCH according to the DCI for paging transmission to be mapped to theEPDCCH, it can obtain the initial transmission or the repeatedtransmission as appropriate.

In the previous description, the paging for initial transmission and thepaging for repeated transmission are multiplexed into a paging message.The number of pagings for repeated transmission may be one or more. Thepagings for repeated transmission may be multiplexed into a pagingmessage. The pagings may be provided per repetition number. Accordingly,multiple repetition numbers can be supported.

Transport channels may be multiplexed as an alternative method. A cellmay multiplex a PCH for initial transmission and a PCH for repeatedtransmission, map a resulting PCH to the same PDSCH, and notify the PCH.The cell may code the PCH for initial transmission and the PCH forrepeated transmission together, and map the resultant to a PDSCH. TheLC-MTC UE can receive the initial transmission or the repeatedtransmission by receiving the multiplexed PCH in the PDSCH.

First Modification of Fourth Embodiment

A first modification will disclose another method for solving theproblems disclosed in the fourth embodiment. The method disclosed in thefourth embodiment causes a problem. An example case where the initialtransmission and the repeated transmission are performed when the SFN is26 and the subframe number is 9 as according to the previous examplewill be described.

Assume herein that the initial transmission is not actually performedand only the repeated transmission is performed when the SFN is 26 andthe subframe number is 9. The LC-MTC UE B to which the initialtransmission may be performed receives the EPDCCH through detection withthe MTC-PI-RNTI. Then, the LC-MTC UE B receives the PDSCH to which thepaging is mapped, according to the paging DCI of the EPDCCH. However,since the initial transmission is not actually performed, the pagingmapped to this PDSCH is the one for repeated transmission to the LC-MTCUE A.

Thus, the LC-MTC UE B to which the initial transmission may be performedhas to receive the PDSCH to obtain the paging, even when no actualinitial transmission is performed. The reception operation is wastefulif no actual initial transmission is performed. In other words, aproblem with increase in power consumption of the LC-MTC UE occurs.

The first modification will disclose a method for solving this problem.The RNTI to be used for the EPDCCH for repeated transmission is madedifferent from the RNTI to be used for the EPDCCH for initialtransmission. The DCI for repeated transmission and the DCI for initialtransmission are masked by the different RNTIs.

In the example paging, the RNTIs may be an MTC-PI-F-RNTI for initialtransmission and an MTC-PI-R-RNTI for repeated transmission. The LC-MTCUE may search for the EPDCCH using the MTC-PI-F-RNTI on a subframe forinitial transmission, and the EPDCCH using the MTC-PI-R-RNTI on asubframe for repeated transmission to receive the respective paging DCIitems.

Accordingly, the LC-MTC UE does not need to receive the PDSCH to whichthe pagings for the other UEs are mapped to obtain the pagings when noactual transmission is performed. Accordingly, increase in powerconsumption of the LC-MTC UE can be prevented. The other UEs are UEsexcluding UEs to which the pagings are transmitted on the same PFs/POsas those of the own UE (hereinafter may be referred to as “intra paginggroup UEs”).

The RNTIs may be provided as many as the number of the repetitions. Whenthe number of the repetitions is 4, for examples, the RNTIs may be anMTC-PI-F-RNTI for initial transmission, an MTC-PI-R1-RNTI for the firstrepeated transmission, an MTC-PI-R2-RNTI for the second repeatedtransmission, an MTC-PI-R3-RNTI for the third repeated transmission, andan MTC-PI-R4-RNTI for the fourth repeated transmission. An upper limitof the number of the repetitions may be set, and the RNTIs may bedetermined according to the upper limit. These values of the RNTIs maybe statically predetermined, for example, in a standard.

The resources of the EPDCCH may be different or identical between theinitial transmission and the repeated transmission. Even when theresources of the EPDCCH are identical, the RNTI to be used for theEPDCCH for repeated transmission is made different from the RNTI to beused for the EPDCCH for initial transmission, and the DCI for repeatedtransmission and the DCI for initial transmission are masked by thedifferent RNTIs.

Accordingly, when the paging DCI for the own LC-MTC UE exists, theLC-MTC UE can receive the DCI. Accordingly, since the LC-MTC UE canreceive the PDSCH to which the paging for the own UE is mapped and doesnot have to receive the PDSCH to which the pagings for the other UEs aremapped, increase in power consumption of the LC-MTC UE can be prevented.

FIGS. 18 and 19 are conceptual diagrams of subframes each including aninitial transmission and the repealed transmission of the EPDCCHaccording to the first modification of the fourth embodiment. Accordingto the example illustrated in FIG. 15, the subframes are subframes whoseSFN is 26 and whose subframe number is 9. In FIGS. 18 and 19, thevertical side represents a frequency, and the horizontal side representsa time. The hatch lines represent the resources of the EPDCCH. FIG. 18illustrates a case where a resource of the EPDCCH for initialtransmission is identical to a resource of the EPDCCH for repeatedtransmission. FIG. 19 illustrates a case where the resource of theEPDCCH for initial transmission is different from the resource of theEPDCCH for repeated transmission.

In FIG. 18, initial DCI (IN(B)) and repeated DCI (RP#1(A)) are mapped toone EPDCCH resource (hereinafter may be referred to as an “EPDCCH forpaging”) 181. The DCI for initial transmission and the DCI for repeatedtransmission are separately masked by different RNTIs. The DCI forinitial transmission is masked by the MTC-PI-F-RNTI. Since therepetition number is 1, the DCI for repeated transmission is masked bythe MTC-PI-R1-RNTI.

The LC-MTC UE A recognizes that the transmission whose SFN is 26 andwhose subframe number is 9 is a transmission with the repetitionnumber 1. Thus, the LC-MTC UE A can detect the resource of the EPDCCH onthe subframe with the MTC-PI-R1-RNTI, and receive the DCI for repeatedtransmission when the DCI for repeated transmission exists.

The LC-MTC UE A receives the PDSCH to which the paging for the own UE ismapped, according to the received DCI. Accordingly, the LC-MTC UE A doesnot have to receive the PDSCH to which the pagings for the other UEs,for example, the LC-MTC UE B are mapped. Thus, increase in powerconsumption of the LC-MTC UE can be prevented.

The LC-MTC UE B recognizes that the transmission whose SFN is 26 andwhose subframe number is 9 is the initial transmission. Thus, the LC-MTCUE B can detect the resource of the EPDCCH on the subframe with theMTC-PT-F-RNTI, and receive the DCI for repeated transmission when theDCI for repeated transmission exists.

The LC-MTC UE B receives the PDSCH to which the paging for the own UE ismapped, according to the received DCI. Accordingly, the LC-MTC UE B doesnot have to receive the PDSCH to which the pagings for the other UEs,for example, the LC-MTC UE A are mapped. Thus, increase in powerconsumption of the LC-MTC UE can be prevented.

In FIG. 19, an EPDCCH resource for initial transmission (hereinafter maybe referred to as an “initial paging transmission EPDCCH”) 182 isdifferent from an EPDCCH resource for repeated transmission (hereinaftermay be referred to as a “repeated paging transmission EPDCCH”) 183. TheDCI for initial transmission (IN(B)) and the DCI for repeatedtransmission (RP#1 (A)) may be separately masked by different RNTIs. TheDCI for initial transmission is masked by the MTC-PI-F-RNTI. Since therepetition number is 1, the DCI for repeated transmission is masked bythe MTC-PI-R1-RNTI.

The LC-MTC UE A can detect the resource of the EPDCCH for the repetitionnumber 1 of the own UE on the subframe with the MTC-PI-R1-RNTI, andreceive the DCI for repeated transmission when the DCI for repeatedtransmission exists. The LC-MTC UE A receives the PDSCH to which thepaging for the own UE is mapped, according to the received DCI.Accordingly, the LC-MTC UE A does not have to receive the PDSCH to whichthe pagings for the other UEs, for example, the LC-MTC UE B are mapped.Thus, increase in power consumption of the LC-MTC UE can be prevented.

Thus, the LC-MTC UE B can detect the resource of the EPDCCH for initialtransmission of the own UE on the subframe with the MTC-PI-F-RNTI, andreceive the DCI for repeated transmission when the DCI for repeatedtransmission exists. The LC-MTC UE B receives the PDSCH to which thepaging for the own UE is mapped according to the received DCI.Accordingly, the LC-MTC UE B does not have to receive the PDSCH to whichthe pagings for the other UEs, for example, the LC-MTC UE A are mapped.Thus, increase in power consumption of the LC-MTC UE can be prevented.

According to the method disclosed in the first modification, when thesubframe for initial paging transmission is identical to the subframefor repeated transmission and only the transmissions for the own UE areperformed, the LC-MTC UE receives the PDSCH to which the paging for theown UE is mapped. Thus, increase in power consumption of the LC-MTC UEcan be prevented.

When the resources to which the EPDCCH is mapped for the initialtransmission and the respective repetition numbers are clearly differentfrom one another within a subframe, the number of the RNTIs may be one.Specifically, the RNTI may be an MTC-PI-RNTI. The LC-MTC UE may detect apredetermined resource of an EPDCCH for initial transmission with theMTC-PI-RNTI, and detect a predetermined resource of an EPDCCH for eachof the repetition numbers with the MTC-PI-RNTI.

Since the resources to which the EPDCCH is mapped for the initialtransmission and the respective repetition numbers are different fromone another, the LC-MTC UE can receive the EPDCCH depending on receptionof the initial transmission or the repeated transmission. Thus, onlywhen the transmission for the own UE is performed, the UE can receivethe PDSCH to which the paging for the own UE is mapped. Accordingly,increase in power consumption of the LC-MTC UE can be prevented.

The methods disclosed in the fourth embodiment and the firstmodification thereof may be applied to a case where repetitions areperformed and an RNTI is used in common among the LC-MTC UEs. Forexample, the methods may be applied to notification of the SI, RAR, etc.Here, the same advantages as those according to the fourth embodimentand the first modification thereof may be produced.

The first modification will disclose another method for solving theproblems. Although the RNTIs are provided as many as the number of theinitial transmission and the number of repetitions in the disclosedmethod above, the RNTIs may be provided separately for the LC-MTC UEs asan alternative method. The DCI for initial transmission and the DCI forrepeated transmission may be masked by an RNTI provided for each of theLC-MTC UEs. The LC-MTC UE may search for both the EPDCCH to which theDCI for initial transmission is mapped and the EPDCCH to which the DCIfor repeated transmission is mapped, using the RNTI of the own UE, andreceive the DCIs. Accordingly, the LC-MTC UE can obtain the pagings forthe own UE by receiving the PDSCH according to the received DCIs.

In the pagings, there may be UEs having the same PFs/POs as those of theown UE. The UEs are the intra paging group UEs. Thus, the RNTI may beprovided not for each of the LC-MTC UEs but for each paging group. Thepaging DCI for the paging group having the same PFs/POs may be masked bythe RNTI.

The following two methods (1) and (2) will be disclosed as a method forrecognizing the RNTI for each of the UEs or for each paging group by theLC-MTC UE.

(1) The RNTI is notified by RRC signaling; here, the RNTI may benotified in the initial access or in a TAU. The RNTI for each of theLC-MTC UEs or for each paging group may be common among cells in a TA.

Accordingly, even when the LC-MTC UE changes a cell to be camped on inRRC_Idle and selects a cell in the same TA, the RNTI can continue to beused. When the LC-MTC UE selects a cell in a different TA, the cellperforms an initial access or a TAU process. Thus, a valid RNTI can benewly obtained in the TA.

(2) A method for deriving an RNTI for each of the UEs or for each paginggroup is predetermined; the deriving method may be predetermined, forexample, in a standard. Specifically, a derivation function may beprovided. The derivation function may be a function using at least oneof a PF and a PO as an input parameter. Examples of the function mayinclude functions using UE identifiers such as a UE-ID, an IMSI, and as-TMSI as input parameters.

Accordingly, the LC-MTC UE can recognize the RNTI for each of the UEs orfor each paging group. Thus, the LC-MTC UE may search for both theEPDCCH to which the DCI for initial transmission is mapped and theEPDCCH to which the DCI for repeated transmission is mapped, using theRNTI of the own UE, and receive the DCIs. Accordingly, the LC-MTC UE canobtain the pagings for the own UE by receiving the PDSCH according tothe received DCIs.

Fifth Embodiment

The first embodiment describes the on-going study on the new methods fornotifying the SI to the LC-MTC UEs that support the reduced bandwidth.Provision of an MTC-SIB that is an SI for the LC-MTC UE has beenproposed as a method for transmitting the SI for the LC-MTC UE (seeNon-Patent Document 13). Moreover, determining six resource blocks atthe center of the system bandwidth as resources to be used fortransmitting an MTC-SIB has been proposed as a method for transmittingthe MTC-SIB (see Non-Patent Documents 10 and 13).

However, transmission of the St for the LC-MTC UE using a particularresource is susceptible to the frequency fading, thus causing a problemwith degradation in reception quality.

The fifth embodiment will disclose another method for transmitting theSI for the LC-MTC UE.

An SIB including the ST for the LC-MTC UE is provided. Here, the SIB isreferred to as an SIB-MTC. The SIB-MTC is mapped to a PDSCH. The controlinformation for the PDSCH to which the SIB-MTC is mapped (hereinaftermay be referred to as “SIB-MTC DCI”) is mapped to an EPDCCH. Examples ofthe SIB-MTC DCI include the scheduling information on the PDSCH to whichthe SIB-MTC is mapped, etc.

An RNTI for masking the control information for the PDSCH to which theSIB-MTC is mapped on the EPDCCH may be an SI-RNTI. Alternatively, theRNTI may be newly provided for the LC-MTC UE. The RNTI may be, forexample, an MTC-SI-RNTI. Distinction from the conventional UEs isenabled by newly providing the RNTI for the LC-MTC UE, for example, theMTC-SI-RNTI. Using the MTC-SI-RNTI in detecting control information, thecontrol information can be identified as that for the LC-MTC UE, and amalfunction can be reduced.

A SIB DCI for the conventional UEs (legacy UEs) may be transmitted usingthe PDCCH, and a SIB-MTC DCI for the LC-MTC UE may be transmitted usingthe EPDCCH. Here, the SIB-MTC DCI to be mapped to the EPDCCH may bemasked by the MTC-PI-RNTI.

When the EPDCCH is used for transmitting the SIB-MTC DCI, it is unclearby which radio frame, by which subframe, or on which resource of thesubframe the EPDCCH is transmitted. Thus, the LC-MTC UE cannot receivethe EPDCCH.

Non-Patent Document 12 discloses a method for solving this problem.Specifically, Non-Patent Document 12 discloses a method for schedulingthe EPDCCH to which the SIB-MTC DCI is mapped. The method is a methodfor mapping, into six resource blocks at the center of the carrier, theEPDCCH for common message that includes SIBs, pagings, and an RAR, or amethod for including, in an MIB, information indicating whether theresource blocks of the EPDCCH are allocated at predetermined positionsor frequency hopping is performed.

However, when the resources to which the SIB-MTC EPDCCH is mapped arefixed to the six resource blocks at the center of the carrier, a problemwith degradation in reception quality occurs due to the susceptibilityto the frequency fading. Furthermore, when the frequency hopping isperformed, how to notify a frequency hopping pattern comes intoquestion.

When the information is included in the MIB and notified, an amount ofinformation in the MIB increases. Furthermore, since the MIB isrepeatedly notified, the amount, of resources required for thenotification will become excessive. Thus, a problem with decrease inefficiency of resource usage occurs.

The fifth embodiment will disclose a method for solving these problems.The resources on which the EPDCCH is transmitted are predetermined, forexample, in a standard. Here, the SIB-MTC DCI is mapped to the EPDCCH.

The following nine examples (1) to (9) are disclosed as examples ofinformation on the resources on which the EPDCCH is to be transmitted.

(1) A period; the period may be provided on a radio frame unit basis oron a subframe unit basis

(2) An offset; the offset may be an offset from a subframe number 0 in aradio frame number 0. The offset may be provided at least one of on aradio frame unit basis, on a subframe unit basis, and on a symbol unitbasis.

(3) The number of resource blocks (RBs)

(4) Allocation of the RBs; the first RB number may be used.

(5) A configuration of a reference signal (RS); a sequence of the RSs orthe sequence number thereof may be used.

(6) The number of repetitions

(7) The frequency hopping mode

(8) A frequency hopping pattern

(9) A combination of (1) to (8) above

The information on the resources on which the EPDCCH is to betransmitted may be any as long as the LC-MTC UE can identify a resourceto which the EPDCCH is mapped. The information may be schedulinginformation on the EPDCCH. As such, predetermining the information, forexample, in a standard prevents increase in the amount of information inthe MIB, and can prevent decrease in the efficiency of resource usage.

The information on the resources of the EPDCCH to which the SIB-MTC DCIis mapped may have multiple options. Information groups on the resourceson which the EPDCCH is to be transmitted may have multiple options. Theinformation on the resources of the EPDCCH to which the SIB-MTC DCI ismapped or the information groups on the resources on which the EPDCCH isto be transmitted are made to have multiple options, so that a cell canchange a resource on which the EPDCCH is transmitted, depending on aradio propagation state. Here, the SIB-MTC DCI is mapped to the EPDCCH.

Accordingly, a communication system resilient to change in the radiopropagation state can be built. Furthermore, when the repetition ofreception of EPDCCH to which the SIB-MTC DCI is mapped is performed, thenumber of the repetitions can be reduced. Thus, the power consumption ofthe LC-MTC UE can be reduced.

However, mere provision of the groups does not allow the LC-MTC UE torecognize which group is to be used. Here, the LC-MTC UE may receive theresources on which the EPDCCH for all of the groups is transmitted anddetect the SIB-MTC DCI with the MTC-PI-RNTI, according to theinformation on all of the groups. However, reception of the EPDCCHs forall of the groups complicates the operations of the LC-MTC UE andincreases the power consumption.

In order to solve such a problem, an indicator associated with theinformation on the resource of each of the EPDCCHs may be provided. Anindicator associated with each of the information groups on theresources on which the EPDCCH is transmitted may be provided. Theindicators and information on the resources of the EPDCCH for each ofthe groups are predetermined in a table, for example, in a standard. TheLC-MTC UE stores the table.

The method disclosed in the third modification of the third embodimentmay be applied to a method for notifying, by a cell, the LC-MTC UE ofwhich information on the resource of the EPDCCH is valid. The sameadvantages as those of the third modification of the third embodimentcan be produced.

Furthermore, a method for deriving information on the resources on whichthe EPDCCH is transmitted may be predetermined as an alternative method.Here, the SIB-MTC DCI is mapped to the EPDCCH. The method disclosed inthe third modification of the third embodiment may be applied to thismethod. Accordingly, the same advantages as those of the thirdmodification of the third embodiment can be produced.

The fifth embodiment will disclose another method for obtaining, by theLC-MTC UE, information on the scheduling of the EPDCCH to which theSIB-MTC DCI is mapped. In the information on the scheduling of theEPDCCH, information on the scheduling in time direction and the otherinformation on the scheduling will be treated separately.

The information on the scheduling in time direction may be staticallypredetermined, for example, in a standard. The information may have oneoption or multiple options. Alternatively, a cell may notify theinformation on the scheduling in time direction by an MIB. The methodusing the indicators as disclosed in the third modification of the thirdembodiment may be applied to the case where the information has multipleoptions.

The other information on the scheduling may be assumed to have multipleoptions and notified by the MIB. The method using the indicators asdisclosed in the third modification of the third embodiment may beapplied thereto. Alternatively, the method of determining the derivationmethod in advance may be applied thereto. The information may be derivedusing a UE identifier (UE-ID) of the LC-MTC UE as an input parameter ofa derivation function. Examples of the information on the scheduling intime direction include a period and an offset.

Accordingly, the same advantages as those of the third modification ofthe third embodiment can be produced.

With the fifth embodiment, the LC-MTC UE can receive the EPDCCH to whichthe SIB-MTC DCI is mapped. Furthermore, it is possible to detect thepresence or absence of the SIB-MTC DCI. If the SIB-MTC DCI exists, theLC-MTC UE can receive the SIB-MTC DCI.

Although mapping the SIB-MTC DCI for the LC-MTC UE to the EPDCCH isdisclosed, the SIB-MTC DCI for the LC-MTC UE may be mapped not only tothe EPDCCH but to a physical downlink control channel using anarrow-bandwidth resource. The physical downlink control channel may beany physical downlink control channel configured within a bandwidth atwhich the LC-MTC UEs that support the reduced bandwidth are capable ofreception.

For the LC-MTC UEs that support the coverage enhancement, the method forrepeatedly transmitting the PDCCH to which the paging downlink controlinformation is mapped, the repeated paging transmission method, and arelationship between these methods may be applied to a method forrepeatedly transmitting the EPDCCH to which the SIB-MTC DCI is mapped, arepeated SIB-MTC transmission method, and a relationship between thesemethods.

Accordingly, the LC-MTC UEs that support the coverage enhancement canreceive the SIB-MTC downlink control information, and the SIB-MTC usingthe SIB-MTC downlink control information.

First Modification of Fifth Embodiment

A time resource of the EPDCCH to which the paging DCI is mapped may beidentical to a time resource of the EPDCCH to which the SIB-MTC DCI ismapped. Examples of a method for indicating the time resource includeusing a radio frame number and a subframe number. The radio frame numberand the subframe number of the EPDCCH to which the paging DCI is mappedare set identical to a radio frame number and a subframe number of theEPDCCH to which the SIB-MTC DCI is mapped, respectively.

Furthermore, the number of repetitions of the EPDCCH to which the pagingDCI is mapped may be identical to the number of repetitions of theEPDCCH to which the SIB-MTC DCI is mapped. The number of repetitions forthe LC-MTC UE supporting the coverage enhancement is determineddepending on a location and a radio propagation environment of theLC-MTC UE.

Thus, when EPDCCHs are transmitted on the same subframe by the cell withthe same number of repetitions, the LC-MTC UE can receive the EPDCCHs towhich the respective DCIs are mapped without degradation in thereception quality.

Since the LC-MTC UE in the RRC_Idle state receives the EPDCCH to whichthe SIB-MTC DCI is mapped, accordingly, it can receive the EPDCCH towhich the paging DCI is mapped. Thus, a period during which the LC-MTCUE performs a receiving operation can be shortened, and the powerconsumption can be reduced.

A period of an EPDCCH to which the paging DCI is mapped may be anintegral submultiple or an integer multiple of a period of an EPDCCH towhich the SIB-MTC DCI is mapped. Accordingly, the number of receptionoperations can be reduced more than that when the transmission timingsof both of the EPDCCHs are not correlated with each other. Accordingly,the reception period can be shortened and the power consumption can bereduced.

Particularly, when the period of the EPDCCH to which the paging DCI ismapped is an integer multiple of the period of the EPDCCH to which theSIB-MTC DCI is mapped, the power consumption of the LC-MTC UE can befurther reduced. The LC-MTC UE that has once received the SIB-MTC doesnot have to receive the SIB-MTC until SI modification is notified by thepaging.

Thus, setting a paging cycle to the integer multiple of the period ofthe SIB-MTC eliminates the need for receiving the SIB-MTC between pagingcycles. Furthermore, the reception of the SIB-MTC can be performedtogether with the reception of paging. Thus, the power consumption ofthe LC-MTC UE can be reduced.

The periods are statically predetermined, for example, in a standard.Alternatively, the periods may be notified by being included in the MIB.It is possible that values of the periods and indicators indicating thevalues are listed in a table, the table is statically predetermined, forexample, in a standard, and an MIB including the indicators is notified.The method disclosed in the third modification of the third embodimentor the fifth embodiment may be applied thereto.

The paging DCI and the SIB-MTC DCI may be mapped within the same EPDCCH.The EPDCCH includes DCIs. The SIB-MTC DCI is masked by the MTC-SI-RNTI,and mapped to the EPDCCH. The paging DCI is masked by the MTC-PI-RNTI,and mapped to the EPDCCH.

The LC-MTC UE can obtain the SIB-MTC DCI by detecting the EPDCCH withthe MTC-SI-RNTI. Furthermore, the LC-MTC UE can obtain the paging DCI bydetecting the EPDCCH with the MTC-PI-RNTI.

Accordingly, only one resource for the EPDCCH may be detected by eachRNTI with the timing of transmission of the EPDCCH. Thus, the receptionperiod for the LC-MTC UE can be further shortened and the powerconsumption thereof can be reduced.

Here, the timing of the EPDCCH to which the paging DCI is mapped doesnot conform to the conventional PFs/POs. The timing of the EPDCCH towhich the paging DCI is mapped may be predetermined, for example, in astandard. The time resource of the EPDCCH to which the paging DCI ismapped may be predetermined to be identical to the time resource of theEPDCCH to which the SIB-MTC DCI is mapped.

Accordingly, the LC-MTC UE can recognize the timing of the EPDCCH towhich the paging DCI is mapped.

Alternatively, a function for deriving a radio frame (PF) and a subframe(PO) of the EPDCCH to which the paging DCI is mapped from the timeresource of the EPDCCH to which the SIB-MTC DCI is mapped may be newlyprovided. The UE identifier (UE-ID) of the LC-MTC UE may be an inputparameter of the derivation function. Accordingly, the subframes onwhich pagings are transmitted to a large number of the LC-MTC UEs can bedispersed.

Although the EPDCCH to which the paging DCI is mapped and the EPDCCH towhich the SIB-MTC DCI is mapped are disclosed, the paging DCI and theSIB-MTC DCI may be mapped not only to the EPDCCH but any physicaldownlink control channel using a narrow-bandwidth resource. The physicaldownlink control channel may be any physical downlink control channelconfigured within a bandwidth at which the LC-MTC UEs that support thereduced bandwidth are capable of reception.

Sixth Embodiment

The transmission power of a conventional uplink channel (PUSCH, PUCCH)is derived using a path loss (PL) as indicated below (see Non-PatentDocument 14).Transmission power of uplink channel=f(x), x=PL

The path loss (PL) is derived using information on the transmissionpower to be notified from a cell to a UE and the received power measuredby the UE. The repeated transmission of the uplink channel by the LC-MTCUEs requiring the coverage enhancement is being studied. The sixthembodiment will disclose a method for deriving the transmission power ofan uplink channel when the LC-MTC UE performs the repeated transmission.

A value obtained by dividing the PL derived by an LC-MTC UE by the totalnumber of transmissions of an uplink channel is newly provided. Thevalue is referred to as a PL-R herein. The total number of transmissionsis a sum of the initial and repeated transmissions. The PL-R is used forderiving the transmission power of the uplink channel instead of theconventional PL. Thus, the transmission power of the uplink channel isderived as indicated below.Transmission power of uplink channel=f(x), x=PL−R=PL/the total number oftransmissions

When the PL is derived in the conventional method, for example, thevalue of the PL derived by an LC-MTC UE at an enhanced coverage edge islarger than the value of the PL derived by a UE at a normal coverageedge. Thus, when the transmission power of the uplink channel is derivedusing the PL derived in the conventional method, the transmission powerof the uplink channel of the LC-MTC UE at the enhanced coverage edge islarger than that of the UE at the normal coverage edge. The repeatedtransmission with the larger transmission power of the uplink channelexcessively increases the received power of a cell.

Thus, with the method disclosed in the sixth embodiment, when an LC-MTCUE performs the repeated transmission of an uplink channel, the receivedpower of the cell can be proper. Furthermore, since the LC-MTC UE canreduce the transmission power of the uplink channel, the powerconsumption can be reduced.

When the LC-MTC UE performs the repeated transmission of the uplinkchannel, the next repeated transmission may be performed withoutreceiving any acknowledgement of the uplink channel, for example, Ack orNack, in response to the preceding transmissions. Since the repeatedtransmission of the uplink channel can be performed without receivingthe acknowledgement on a per transmission basis, a control delay can beshortened. Here, a cell does not have to transmit the acknowledgement tothe LC-MTC UE.

Here, the method for deriving the transmission power of the uplinkchannel disclosed in the sixth embodiment may be used. The LC-MTC UEperforms all the transmissions including the initial and repeatedtransmissions. Thus, the LC-MTC UE can reduce the transmission powermore than by the entire transmissions with a larger amount of power, andreduce the power consumption. Furthermore, the cell can obtain theproper received power by combination of the initial and repeatedtransmissions from the LC-MTC UE.

When the LC-MTC UE performs the repeated transmission of the uplinkchannel, it may receive acknowledgements of the uplink channel inresponse to the preceding transmissions. The cell transmits theacknowledgements in response to the transmissions of the uplink channelfrom the LC-MTC UE. Here, the LC-MTC UE may use a conventional methodfor deriving the transmission power of the uplink channel. Since theLC-MTC UE can perform the transmission with the transmission powermatching the PL, the cell may receive the uplink channel with a fewernumber of repetitions. Here, the cell transmits the acknowledgement tothe LC-MTC UE. The LC-MTC UE that has received the acknowledgement stopsthe repeated transmission.

Thus, the LC-MTC UE can perform the uplink channel transmission with afewer number of repetitions. Accordingly, the efficiency of resourceusage can be improved.

An offset value may be newly provided to derive a path loss for theLC-MTC UE. When the LC-MTC UE derives the path loss, the offset valuemay be used. The offset value may be set for each cell or for each UE.When the offset value is set for each cell, the cell broadcasts it asthe SI for the LC-MTC UE. Alternatively, the cell may notify the LC-MTCUEs separately of offset values using the RRC signaling. When the offsetvalue is set for each UE, the cell may notify the LC-MTC UEs separatelyof offset values using the RRC signaling.

An offset value may be newly provided to derive the transmission powerof an uplink channel for the LC-MTC UE as an alternative method. Whenthe LC-MTC UE derives the transmission power of the uplink channel, theoffset value may be used. The offset value may be set for each cell orfor each UE. The notification method from the cell to the LC-MTC UE maybe applied thereto. Furthermore, the two methods may be combined foruse.

Accordingly, the settings on the LC-MTC UE can be changed differentlyfrom those of the conventional UEs. Furthermore, the transmission powerof the LC-MTC UE can be flexibly set depending on a radio propagationenvironment and an interference condition. Accordingly, a stablecommunication system can be built even in a coexistence of theconventional UEs and the LC-MTC UEs.

Seventh Embodiment

Furthermore, the need for systems using an unlicensed spectrum that is aspectrum that has not been licensed as a tool for complementing alicensed spectrum that is a spectrum that has been licensed isincreasing. Examples of the unlicensed spectrum include the ISM bandsused for wireless LAN, etc. 3GPP is studying Licensed-Assisted Access(LAA) using the unlicensed spectrum as a tool for complementing thelicensed spectrum, with the LTE. The unlicensed spectrum is only the DL,or UL and DL.

When an unlicensed spectrum is used, a fair coexistence method with theother systems using the unlicensed spectrum is necessary.

Thus, LAA needs to have at least the following five functions (1) to(5).

(1) Listen-before-talk (clear channel assessment)

(2) Discontinuous transmission on a carrier with a limited maximumtransmission duration

(3) Dynamic frequency selection for radar avoidance in certainbands/regions

(4) Carrier selection

(5) Transmission power control (TPC)

3GPP is studying solutions for satisfying these requirements. Non-PatentDocument 15 discloses, for example, two methods (1) and (2) below on thedata transmission.

(1) Frame-Based Equipments (FBE)

The clear channel assessment (CCA) is performed with the frame boundarytiming. When the channel is clear, data is transmitted. When the channelis busy, the CCA is again performed with the next frame boundary timing.

(2) Load-Based Equipments (LBE)

The CCA is consecutively performed. When the channel is clear apredetermined number of times, data is immediately transmitted.

Data cannot be consecutively transmitted for a long period over anunlicensed spectrum to ensure the fairness with the other systems toenable the coexistence. It has been proposed that a cell performsdiscontinuous transmission when data transmission is necessary and doesnot transmit any when the data transmission is unnecessary. However,when nothing is transmitted from the cell, the UE has a problem withincapability of synchronization or measurement of the unlicensedspectrum.

Thus, a signal for synchronizing with or measuring the unlicensedspectrum is necessary. A signal to be transmitted periodically on afewer number of subframes is being studied as the signal forsynchronizing with or measuring the unlicensed spectrum. For example,application of a discovery signal (DS) for a small cell has beenproposed (see Non-Patent Document 16). The DS transmission is cyclical,and the transmission timing is determined on a subframe unit basis.Furthermore, an eNB notifies, in advance, a UE of settings for DSmeasurement, such as a DS measurement period and an offset. The UEreceives the DS according to the settings for DS measurement notifiedfrom the eNB.

However, such transmission of the signal for synchronizing with ormeasuring the unlicensed spectrum requires avoidance of a collision andensuring the fairness with the other systems to enable the coexistence.Although the fair coexistence method on the data transmission has beenproposed as above, there is no fair coexistence method on the signal forsynchronizing with or measuring such an unlicensed spectrum.

In the case where a cell does not transmit any, the UE does not receivea PDCCH every subframe and detect the presence or absence of thescheduling information on the PDSCH unlike in receiving data. Thus, thefair coexistence method in transmitting data cannot be applied as it is.

Without any ingenuity, the UE has a problem with incapability ofsynchronization or measurement of the unlicensed spectrum.

The method for solving this problem will be disclosed hereinafter.Before transmitting the signal for synchronizing with or measuring theunlicensed spectrum, a cell performs the CCA. The signal forsynchronizing with or measuring the unlicensed spectrum may be the DS.

FIG. 20 is a conceptual diagram illustrating an example in which a celltransmits DSs and a UE measures the DSs over an unlicensed spectrumaccording to the seventh embodiment. The horizontal axis represents atime. A DS 191 represents a duration configured from one subframe or acombination of subframes (hereinafter may be referred to as a “DStransmission duration”). When a DS is configured from a combination ofsubframes, the DS on one of the subframes may be repeated.

FIG. 20 illustrates an example in which the DS transmission duration isconfigured from two subframes. The diagonally hatched subframes aresubframes on which the DS is actually transmitted. A cell periodicallytransmits the DS at intervals of a transmission period (Tds) of the DSover the unlicensed spectrum.

A CCA 192 is certainly performed before the DS is transmitted. When thechannel is clear through the CCA, the DS is transmitted. In FIG. 20, theblank CCA represents a clear channel. The CCA may be performed at aboundary of the subframe on which the DS starts to be transmitted.During the CCA, the DS may not be transmitted. Alternatively, the endtiming of the CCA may be at the boundary of the subframe on which the DSstarts to be transmitted. Accordingly, a cell can transmit the DS.

A cell notifies a UE configuring an unlicensed spectrum of the settingson measurement of the DS over the unlicensed spectrum. The settings onmeasurement of the DS include a DS measurement period (Tmeas_p), anoffset (a measurement start timing), and a DS measurement duration(Tmeas_d).

A UE measures the DS in the DS measurement duration (Tmeas_d) from theoffset. The UE repeatedly measures the DS in the DS measurement duration(Tmeas_d) at intervals of a measurement period (Tmeas_p) of the DS fromthe offset. A cell configures the settings on measurement of the DS overthe unlicensed spectrum. The settings on measurement of the DS may beconfigured by a cell over the unlicensed spectrum or a cell connected tothe UE over a licensed spectrum.

When the cell over the unlicensed spectrum configures the settings, thecell may notify the UE of the settings. Alternatively, the cellconnected to the UE over the licensed spectrum may obtain the settingsfrom a cell over the unlicensed spectrum and notify the UE of thesettings.

When the cell connected to the UE over the licensed spectrum configuresthe settings, the cell may notify the UE of the settings. The cell maynotify the UE of the settings together with information on theconfiguration of the unlicensed spectrum.

The cell may notify the UEs of the settings through dedicated signaling.The RRC signaling may be used. Thus, separate settings are madeavailable for the UEs. Alternatively, the settings may be broadcasted assystem information on the cell. The settings can be configured for eachcell. When the settings are notified to a large number of the UEs, anamount of the information through the dedicated signaling can bereduced.

Accordingly, the UEs configuring the unlicensed spectrum can measure theDS, and synchronize with and measure the unlicensed spectrum.

However, when the channel is not clear through the CCA, the DS cannot betransmitted in the DS transmission duration. When the DS cannot betransmitted, the UE has problems with incapability of receiving the DSin the DS measurement duration (Tmeas_d) notified from the cell and ofsynchronizing with or measuring the unlicensed spectrum.

The method for solving these problems will be disclosed hereinafter. Asecond DS transmission period (DS transmission period 2 (Tds2)) isprovided. When the channel is not clear through the CCA, a cell performsthe CCA again with the DS transmission timing after the second DStransmission period.

The following five examples (1) to (5) are disclosed as specificexamples of the DS transmission period 2.

(1) The DS transmission period 2 is identical to the DS transmissionduration. At the end of the DS transmission duration, the CCA is againperformed.

(2) The DS transmission period 2 is identical to a DS measurementduration configured for a UE.

When the UE cannot receive the DS after the DS measurement duration, itcontinuously measures the DS in the DS measurement duration again.

(3) The DS transmission period 2 is within the DS transmission period.

Furthermore, an upper limit of the number of the DS transmissionsthrough the CCA may be provided. A period for the DS transmissionshaving the upper limit through the CCA may be within the DS transmissionperiod. The DS transmission period 2 may be an integral submultiple ofthe DS transmission period.(4) The DS transmission period 2 is identical to the DS transmissionperiod.(5) A combination of (1) to (4) above

The settings of the second DS transmission period may be configured by acell over the unlicensed spectrum or a cell connected to the UE over thelicensed spectrum. Accordingly, the settings can be flexibly configuredin consideration of a radio propagation environment and the coexistencewith the other systems.

A method for measuring the DS by the UE will be disclosed hereinafter.Since the UE does not know when the DS is transmitted due to the CCA, aDS measurement window for the CCA is provided. Assuming that the DS istransmitted during a period of the DS measurement window for the CCA,the UE measures the DS. Examples of the DS measurement window for theCCA may include a second measurement duration of the DS (a DSmeasurement duration 2 (Tmeas_d2)).

The DS measurement duration 2 may be configured according to the DStransmission period 2 and a setting of the number of the DStransmissions through the CCA. The DS measurement duration 2 may beconfigured longer than the period for the DS transmissions having theupper limit through the CCA. The UE receives the DSs during the DSmeasurement duration and the DS measurement duration 2. If the UE cannotreceive the DS, it repeatedly receives the DSs for the DS measurementduration during the DS measurement duration 2.

When the UE receives the DS, it may finish receiving the DS even in themiddle of the reception. When the UE receives the DS and is able toperform at least one of the synchronization and measurement of the DS,it may finish receiving the DS even in the middle of the reception. TheUE may finish receiving the DS even in the middle of the DS transmissionduration (one set of the DS transmission). Furthermore, an offset (ameasurement start timing) may be provided as the DS measurement windowfor the CCA. The offset may be an offset from the beginning of the DSmeasurement duration. The offset may be provided on a subframe unitbasis.

A cell configures the DS measurement window for a UE configuring anunlicensed spectrum. The settings of the DS measurement window may beconfigured by a cell over the unlicensed spectrum or a cell connected tothe UE over the licensed spectrum.

When the cell over the unlicensed spectrum configures the settings, thecell may notify the UE of the settings. Alternatively, the cellconnected to the UE over the licensed spectrum may obtain the settingsfrom a cell over the unlicensed spectrum and notify the UE of thesettings. When the cell connected to the UE over the licensed spectrumconfigures the settings, the cell may notify the UE of the settings.

The cell may notify the settings including the setting on themeasurement of the DS over the unlicensed spectrum. Furthermore, thecell may notify the UE of information on whether the CCA is performed onthe DS over the unlicensed spectrum. The cell may notify the UE ofinformation indicating in which method the CCA is performed. The cellmay notify the settings including the setting on the measurement of theDS over the unlicensed spectrum.

The cell may notify the UEs of the settings through dedicated signaling.The RRC signaling may be used. Thus, separate settings are madeavailable for the UEs. Alternatively, the settings may be broadcasted assystem information on the cell. Settings can be configured for eachcell. When the settings are notified to a large number of the UEs, anamount of information through the dedicated signaling can be reduced.

Although the seventh embodiment describes the DS, not limited to the DSbut any signal for synchronizing with or measuring the unlicensedspectrum may be used.

FIG. 21 is an example conceptual diagram illustrating that a celltransmits the DSs and the UE measures the DSs over the unlicensedspectrum according to the seventh embodiment. In CCAs 201, 203, and 205,diagonally hatched CCAs represent that the channel is not clear, and aCCA with no hatching represents that the channel is clear.

In DSs 202, 204, and 206, a diagonally hatched DS representstransmission of the DS, and DSs with no hatching represent notransmission of the DSs.

A cell performs the CCA 201, and does not transmit the DS 202 when thechannel is not clear. When the channel is not clear through the CCA, theCCA 203 is performed again after the DS transmission period 2. When thecell performs the CCA 203 and the channel is not clear again, it doesnot transmit the DS 204 and performs the CCA 205 again after the DStransmission period 2. When the cell performs the CCA 205 and thechannel is clear, it transmits the DS 206.

The cell periodically transmits the DS at intervals of the transmissionperiod (Tds) of the DS over the unlicensed spectrum. The cell certainlyperforms the CCA before transmitting the DS, and follows the disclosedmethod.

The UE measures the DS during the DS measurement duration 2 that is theDS measurement window for the CCA. The UE that has been notified of theDS measurement duration 2 and the DS transmission period 2 mayrepeatedly measure the DS measurement duration and the DSs at the DStransmission period 2 during the DS measurement duration 2. When the UEreceives the DS, it finishes receiving the DS even in the middle of thereception.

In FIG. 21, the UE receives the DS 206, performs at least one of thesynchronization and the measurement, and finishes receiving the DSs.When the UE receives the DS, it measures the DS again after the DSmeasurement period (Tmeas_p). The UE periodically measures the DS atintervals of the DS measurement period (Tmeas_p). The DS is measuredaccording to the disclosed method.

According to the method disclosed in the seventh embodiment, when a celltransmits at least one of a synchronization signal and a measurementsignal over the unlicensed spectrum, even in the case where the channelis not clear, the cell can transmit the signal again. Furthermore,before the cell transmits the DS, even when the channel is not clearthrough the CCA, the UE can receive at least one of the synchronizationsignal and the measurement signal.

Thus, even in such a case, the UE can perform at least one of thesynchronization and the measurement of the unlicensed spectrum.Accordingly, the CCA can be introduced to at least one of thesynchronization signal and the measurement signal for the unlicensedspectrum. Accordingly, it is possible to avoid a collision with theother systems over the unlicensed spectrum, and ensure the fairnesstherewith to enable the coexistence.

First Modification of the Seventh Embodiment

When the channel is not clear through the CCA, transmission is performedon the DS transmission period 2 according to the method disclosed in theseventh embodiment. Thus, the DS is not transmitted during the DStransmission period 2. When the channel is not clear as a result of theCCA, a delay occurs until transmission of the DS. Thus, the UE has adelay in synchronization with and measurement of a cell over theunlicensed spectrum.

The method for solving this problem will be disclosed hereinafter. Whenthe channel is not clear through the CCA, a cell continues to performthe CCA. When the channel is clear, the cell immediately transmits theDS. Alternatively, when the channel becomes clear a predetermined numberof times through the CCA, the cell may immediately transmit the DS. Anupper limit of the number of the DS transmissions through the CCA may beprovided. A period for the DS transmissions having the upper limitthrough the CCA may be set within the DS transmission period.

The method disclosed in the seventh embodiment may be applied to amethod for measuring the DS by the UE. Furthermore, the method disclosedin the seventh embodiment may be applied to a method, by a cell, forconfiguring the DS measurement window to a UE configuring the unlicensedspectrum and to a method for notifying the UE of the configuration.

FIG. 22 is an example conceptual diagram illustrating that a celltransmits the DSs and the UE measures the DSs over the unlicensedspectrum according to the first modification of the seventh embodiment.Since the conceptual diagram of FIG. 22 is similar to the conceptualdiagram of FIG. 21, the same reference numerals will be assigned to thesame structures and the common description thereof will be omitted.

In CCAs 211, diagonally hatched CCAs represent that the channel is notclear, and no hatched CCAs represents that the channel is clear. In DSs212, diagonally hatched DSs represent transmission of the DSs, and DSswith no hatching represent no transmission of the DSs.

When the channel is not clear through a CCA 213, a cell continues toconsecutively perform the CCA. When the channel becomes clear apredetermined number of times through the CCA, the cell immediatelytransmits the DS. The predetermined number of times may be staticallypredetermined, for example, in a standard. Alternatively, thepredetermined number of times may be determined by a core network sideor an operator, and notified to a cell in advance. The predeterminednumber of times is three herein. When the channel is clear for the thirdtime through a CCA 214, the cell transmits a DS 215.

The cell periodically transmits the DS at intervals of the transmissionperiod (Tds) of the DS over the unlicensed spectrum. The cell certainlyperforms the CCA before transmitting the DS, and follows the disclosedmethod.

The UE measures the DS during the DS measurement duration 2 that is theDS measurement window for the CCA. The UE may measure the DS during theDS measurement duration 2 even when the DS measurement duration isnotified. Accordingly, even when the transmission of the DS exceeds ameasurement duration of a UE through the CCA, the UE can measure the DSthrough its measurement during the second DS measurement duration. Whenthe UE receives the DS, it finishes receiving the DS even in the middleof the reception.

In FIG. 22, the UE receives a DS 212, performs synchronization andmeasurement, and finishes receiving the DS. When the UE receives the DS,it measures the DS again after the DS measurement period (Tmeas_p). TheUE periodically measures the DS at intervals of the DS measurementperiod (Tmeas_p). The DS is measured according to the disclosed method.

The method disclosed in the first modification can produce the sameadvantages as described in the seventh embodiment. Furthermore, the cellcan perform the CCA on the DS transmission period 2, without waiting forthe next DS transmission timing. Thus, when the channel is clear throughthe CCA, the cell can immediately transmit the DS. A delay untiltransmission of the DS can be reduced.

Furthermore, the UE can shorten a time for synchronizing with andmeasuring a cell over the unlicensed spectrum. Thus, a control delay canbe reduced. Furthermore, the power consumption of the UE can be reduced.

Although the cell immediately transmits the DS when the channel is clearthrough the CCA, the cell may transmit the DS from the next subframe.The DS may be transmitted from the beginning of the next subframe orafter a predetermined symbol. The predetermined symbol may be notifiedto the UE. The method disclosed in the seventh embodiment may be appliedto a method for notifying the predetermined symbol. When there is a timebetween the end of the CCA and start of the transmission of the next DS,a signal indicating an occupied state may be transmitted during thetime.

Accordingly, it is possible to prevent the other systems from using theunlicensed spectrum during the time. Thus, a cell can transmit the nextDS without a collision with the other systems when starting to transmitthe DS. Furthermore, a delay until transmission of the DS can bereduced.

FIGS. 23 and 24 illustrate example processes until data communicationthrough transmission of the DSs and measurement by the UE as describedin the first modification of the seventh embodiment. FIGS. 23 and 24 areconnected across a border BL1. Since the conceptual diagram of FIGS. 23and 24 is similar to the conceptual diagram of FIG. 22, the samereference numerals will be assigned to the same structures and thecommon description thereof will be omitted.

In CCAs 211, diagonally hatched CCAs represent that the channel is notclear, and CCAs with no hatching represent that the channel is clear. InDSs 212, diagonally hatched DSs represents transmission of the DSs, andDSs with no hatching represent no transmission of the DSs.

A cell #1 is a cell on a licensed spectrum and a cell to which a TU isRRC-connected. A cell #2 is a cell on an unlicensed spectrum. In theexample of FIGS. 23 and 24, the cell #2 configures the DS transmissionsettings. The DS transmission settings include a DS transmission period,an offset (a measurement start timing), a sequence of the DSs, whetherthe CCA is performed, and in which method the CCA is performed.

In Step ST2201, the cell #2 notifies the cell #1 of the DSconfiguration. The cell #1 configures the measurement of the DS over theunlicensed spectrum using the notified DS configuration.

In Step ST2202, the cell #1 notifies the UE of the measurementconfiguration on the DS. The measurement configuration on the DS overthe unlicensed spectrum includes a frequency (carrier frequency) of theunlicensed spectrum, a DS measurement period (Tmeas_p), an offset (ameasurement start timing), and a DS measurement window for the CCA (DSmeasurement duration 2 (Tmeas_d2)). The measurement configuration mayinclude the sequence of the DSs. The measurement configuration mayinclude information on whether the CCA, is performed and in which methodthe CCA is performed. Furthermore, the measurement configuration mayinclude information on a measurement report.

The cell #2 transmits the DS according to the DS configuration whentransmitting no data. The UE that has received the measurementconfiguration on the DS over the unlicensed spectrum from the cell #1 inStep ST2202 measures the DS at the frequency (carrier frequency) of thenotified unlicensed spectrum in Step ST2203. The UE measures the DSduring the DS measurement window for the CCA from the measurement starttiming and repeats it at the DS measurement period at the frequency(carrier frequency) of the notified unlicensed spectrum.

When the UE has received one or more DSs and criteria on the measurementreport is satisfied, the UE notifies the cell #1 of the measurementreport in Step ST2204. Identification of a cell such as a PCI and thereception qualities such as the RSRP and the RSRQ are reported as themeasurement report. The criteria on the measurement report may bepredetermined, for example, in a standard. The criteria include a resultof the measurement on the DSs of the cell #2.

The cell #1 that has received the measurement report from the UEdetermines to configure the cell #2 for the UE using the measurementreport. In Step ST2205, the cell #1 notifies the UE of cell addition.The cell addition includes a cell identifier and a carrier frequency ofa cell to be added that is the cell #2. Furthermore, the cell #1notifies settings on the measurement of the DS of the cell to be added.The settings may be omitted when they are the same as the settings onthe measurement of the DS notified in Step ST2202.

The UE that has received the settings on the measurement of the US inStep ST2205 measures the DS of the cell #2 using the settings andsynchronizes with the cell #2 in Step ST2206. The UE continues tosynchronize with the cell #2 until the cell #1 notifies releasing of thecell #2 to the UE. Furthermore, the measurement may be performed.

In Step ST2207, the cell #1 that has determined the communication withthe UE through the cell #2 notifies the UE that the cell #2 is active(cell activation). The UE that has received the notification startsreceiving the data from the cell #2 in Step ST2210. Since the data maybe transmitted from the cell #2 every subframe, the UE continues toreceive the data until the cell #1 notifies that the cell #2 isdeactivated.

Furthermore, the cell #1 that has determined the communication with theUE through the cell #2 notifies the cell #2 of the instruction toactivate the data transmission (cell activation) in Step ST2208. Thecell #2 that has received the instruction transmits data to the UE inStep ST2209. The UE receives the data from the cell #2.

Accordingly, when at least one of the synchronization signal and themeasurement signal is transmitted over the unlicensed spectrum in astate where a cell over the unlicensed spectrum does not transmit data,the CCA can be introduced before the transmission. Furthermore, evenwhen the CCA is introduced, the UE can receive at least one of thesynchronization signal and the measurement signal over the unlicensedspectrum.

Furthermore, the UE can synchronize with and measure a cell over theunlicensed spectrum, and a cell over a licensed spectrum can add a cellover the unlicensed spectrum and set the cell active. Thus, datacommunication using the cell over the unlicensed spectrum can beperformed.

Furthermore, the LAA using a cell on a licensed spectrum and a cell overan unlicensed spectrum becomes possible. Furthermore, it is possible toavoid a collision with the other systems over the unlicensed spectrum,and ensure the fairness therewith to enable the coexistence.

The embodiments and the modifications herein are merely illustrations ofthe present invention and can be freely combined within the scope of theinvention. Also, any constituent elements of the embodiments and themodifications thereof can be appropriately modified or omitted.Accordingly, even when the various services including a support of theMTC and the use of the unlicensed spectrum are supported, acommunication system that enables improvement in communicationperformance of a communication terminal device can be provided.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE NUMERALS

1301 coverage of a macro eNB (macro cell), 1302 coverage of a small eNB(small cell).

The invention claimed is:
 1. A communication system, comprising: acommunication terminal device; and a base station device configuring atleast one cell configured to perform radio communication with saidcommunication terminal device, wherein said communication terminaldevice includes a narrow-bandwidth terminal device having a narrowercommunication bandwidth narrower than a system bandwidth that can beused by said cell, said narrow-bandwidth terminal device performsdiscontinuous reception for intermittently receiving a signaltransmitted from said cell and determines a reception condition of saidsignal when said narrow-bandwidth terminal device is in an idle statewithin a coverage area of said cell, and said narrow-bandwidth terminaldevice moves out of said coverage area of said cell while continuing toperform said discontinuous reception, when said reception condition ofsaid signal satisfies a predetermined moving condition.
 2. Thecommunication system according to claim 1, wherein said moving conditionis a determination that said signal cannot be received.
 3. Thecommunication system according to claim 1, wherein said moving conditionis a determination that a reception quality of said signal is lower thanor equal to a predetermined moving threshold.
 4. The communicationsystem according to claim 1, wherein said narrow-bandwidth terminaldevice performs a cell selection process upon completion of a period ofsaid discontinuous reception after moving out of said coverage area ofsaid cell.
 5. The communication system according to claim 1, whereinsaid narrow-bandwidth terminal device performs a cell selection processbefore moving out of said coverage area of said cell, when saidreception condition of said signal satisfies a predetermined movingcondition.